style: format code with Black

This commit fixes the style issues introduced in 710a4f0 according to the output
from Black.

Details: None

src/lastversion/repo_holders/mercurial.py

@@ -5,6 +5,7 @@
 
 class MercurialRepoSession(BaseProjectHolder):
     """Mercurial repository holder."""
+
     CAN_BE_SELF_HOSTED = True
     REPO_URL_PROJECT_COMPONENTS = 1