message: Fix the build error of GitHub Actions for macOS.
  *
  * readPlist and writePlistToBytes have been removed since Python 3.9
  +
diff: @@ -43,14 +43,14 @@ index 64d21063..3b878ddf 100755
  - fd = open(source, 'r')
  - lines = fd.read()
  - fd.close()
  -+ plist = plistlib.readPlist(source)
  ++ plist = plistlib.load(source)
  # Insert synthesized key/value pairs (e.g. BuildMachineOSBuild).
  - plist = plistlib.readPlistFromString(lines)
  if keys:
  plist.update(json.loads(keys[0]))
  - lines = plistlib.writePlistToString(plist)
  -+ lines = plistlib.writePlistToBytes(plist).decode('utf-8')
  ++ lines = plistlib.dumps(plist).decode('utf-8')
  # Go through all the environment variables and replace them as variables in
  # the file.
  