standardize config on ruamel.yaml with a YAML 1.2 config

This is a key piece of the ongoing `PUBLISH` _config.yml_ migration. There was uneven implementation of which YAML parser to use, and that could lead to bugs where one parser might read a value one way, and a different parser will read the value a different way. I wanted to be sure that YAML 1.2 would always work.

This makes all code that handles config files use the same `ruamel.yaml` parsers.  This only touches other usages of YAML parsers when there is overlap.  This does not port all of _fdroidserver_ to `ruamel.yaml` and YAML 1.2.  The metadata files should already be YAML 1.2 anyway.

# Conflicts:
#	fdroidserver/lint.py

tests/test_integration.py

@@ -11,13 +11,12 @@ from datetime import datetime, timezone
 from http.server import SimpleHTTPRequestHandler, ThreadingHTTPServer
 from pathlib import Path
 
-from ruamel.yaml import YAML
-
 try:
     from androguard.core.bytecodes.apk import get_apkid  # androguard <4
 except ModuleNotFoundError:
     from androguard.core.apk import get_apkid
 
+from fdroidserver._yaml import yaml, yaml_dumper
 from .shared_test_code import mkdir_testfiles
 
 # TODO: port generic tests that use index.xml to index-v2 (test that
@@ -81,7 +80,6 @@ class IntegrationTest(unittest.TestCase):
     @staticmethod
     def update_yaml(path, items, replace=False):
         """Update a .yml file, e.g. config.yml, with the given items."""
-        yaml = YAML()
         doc = {}
         if not replace:
             try:
@@ -91,7 +89,7 @@ class IntegrationTest(unittest.TestCase):
                 pass
         doc.update(items)
         with open(path, "w") as f:
-            yaml.dump(doc, f)
+            yaml_dumper.dump(doc, f)
 
     @staticmethod
     def remove_lines(path, unwanted_strings):