Bug 1964582 - Add git to distribution part build-packages for snap repackage r=sergesanspaille

Depending on the 'snapcraft' version used by the developper; git may or
may not be installed automatically and this is a bit painful of an
experience. Let's add it ourselves.

Differential Revision: https://phabricator.services.mozilla.com/D247876

python/mozbuild/mozbuild/repackaging/snapcraft_transform.py

@@ -62,6 +62,7 @@ class SnapcraftTransform:
     def repack(self):
         removed = self.keep_non_build_parts()
         self.add_firefox_repack(removed)
+        self.fix_distribution()
         self.change_version(self._version, self._buildno)
         self.change_name(self._appname)
         return yaml.safe_dump(self.snap, sort_keys=False)
@@ -95,6 +96,11 @@ class SnapcraftTransform:
 
         return removed
 
+    def fix_distribution(self):
+        self.snap["parts"]["distribution"].setdefault("build-packages", []).append(
+            "git"
+        )
+
     def add_firefox_repack(self, removed):
         repack_yaml = """
   firefox: