package_checks: output dep lists with proper offset (#3928)

**Summary**

Change loader/dumper to ruamel to enable putting out dependency lists
with proper offset and colon spacing. This way the output can directly
be copied and pasted into the recipe.

Note: I couldn't find a way to do this with pyyaml; Dumper
implementation [adopted from ruamel
docs](https://yaml.readthedocs.io/en/latest/example/#output-of-dump-as-a-string).
I also couldn't get `top_level_colon_align` to work for some reason, so
in cases of very short subpackage names with dependencies the colon
might be placed too far to the left (not 100% sure if there is such a
case in the repo; the "^g++" case happens to perfectly align)

Resolves https://github.com/getsolus/packages/issues/3924

**Test Plan**

Old output `budgie-desktop-branding`:
```
- breeze-cursor-theme
- budgie-backgrounds
- budgie-desktop
- font-hack-ttf
- livecd:
  - budgie-desktop-branding
  - test
- materia-gtk-theme
- materia-gtk-theme-dark
- noto-sans-ttf
- noto-serif-ttf
- papirus-icon-theme
- qtstyleplugins
- solus-artwork
- test
```

New output `budgie-desktop-branding`:
```
    - breeze-cursor-theme
    - budgie-backgrounds
    - budgie-desktop
    - font-hack-ttf
    - livecd :
        - budgie-desktop-branding
        - test
    - materia-gtk-theme
    - materia-gtk-theme-dark
    - noto-sans-ttf
    - noto-serif-ttf
    - papirus-icon-theme
    - qtstyleplugins
    - solus-artwork
    - test
```

Old output `gcc` rundeps:
```
- ^g++: gcc
- ^gfortran:
  - gcc
  - libgfortran
- ^libgcc-32bit: libgcc
- ^libgfortran-32bit: libgfortran
- ^libgomp-32bit:
  - libgcc-32bit
  - libgomp
- ^libstdc++-32bit: libstdc++
- mpc
- mpfr
- test
```

New output `gcc` rundeps:
```
    - ^g++ : gcc
    - ^gfortran :
        - gcc
        - libgfortran
    - ^libgcc-32bit : libgcc
    - ^libgfortran-32bit : libgfortran
    - ^libgomp-32bit :
        - libgcc-32bit
        - libgomp
    - ^libstdc++-32bit : libstdc++
    - mpc
    - mpfr
    - test
```

**Checklist**

- [x] Package was built and tested against unstable

common/CI/package_checks.py

@@ -11,12 +11,12 @@ import sys
 from dataclasses import dataclass
 from datetime import datetime, timezone
 from enum import Enum
+from ruamel.yaml import YAML
+from ruamel.yaml.compat import StringIO
 from typing import Any, Callable, Dict, List, Optional, TextIO, Tuple, Union
 from urllib import request
 from xml.etree import ElementTree
 
-import yaml
-
 """Package is either a Package YML file or Pspec XML file."""
 Package = Union['PackageYML', 'PspecXML']
 
@@ -30,7 +30,9 @@ class PackageYML:
     """Represents a Package YML file."""
 
     def __init__(self, stream: Any):
-        self._data = dict(yaml.safe_load(stream))
+        yaml = YAML(typ='safe', pure=True)
+        yaml.default_flow_style = False
+        self._data = dict(yaml.load(stream))
 
     @property
     def name(self) -> str:
@@ -105,7 +107,8 @@ class Config:
 
     @staticmethod
     def load(stream: Any) -> 'Config':
-        return Config(**yaml.safe_load(stream))
+        yaml = YAML(typ='safe', pure=True)
+        return Config(**yaml.load(stream))
 
     def __post_init__(self) -> None:
         self.freeze = FreezeConfig(**self.freeze)  # type: ignore
@@ -409,7 +412,9 @@ class Homepage(PullRequestCheck):
 
     def _includes_homepage(self, file: str) -> bool:
         with self._open(file) as f:
-            return 'homepage' in yaml.safe_load(f)
+            yaml = YAML(typ='safe', pure=True)
+            yaml.default_flow_style = False
+            return 'homepage' in yaml.load(f)
 
 
 class PackageBumped(PullRequestCheck):
@@ -467,8 +472,18 @@ class PackageDependenciesOrder(PullRequestCheck):
         exp = self._sorted(cur)
 
         if cur != exp:
+            class Dumper(YAML):
+                def dump(self, data: Any, stream: Optional[StringIO] = None, **kw: int) -> Any:
+                    self.default_flow_style = False
+                    self.indent(offset=4, sequence=4)
+                    self.prefix_colon = ' '  # type: ignore[assignment]
+                    stream = StringIO()
+                    YAML.dump(self, data, stream, **kw)
+                    return stream.getvalue()
+
+            yaml = Dumper(typ='safe', pure=True)
             return Result(file=file, level=self._level, line=self.file_line(file, '^' + deps + r'\s*:'),
-                          message=f'{deps} are not in order, expected: \n' + yaml.safe_dump(exp))
+                          message=f'{deps} are not in order, expected: \n' + yaml.dump(exp))
 
         return None