fix(changelogs): Don't look for Fedora Version (#324)

Since this was adapted from bazzite/bluefin, they looked for the string
".fc" for figuring out the fedora version.

Centos has EL. This changes it to that and has the prefix CS for the
title instead of F.

.github/changelogs.py

@@ -356,7 +356,7 @@ def generate_changelog(
             linux: str = next(iter(manifests.values()))["Labels"][
                 "ostree.linux"
             ]
-            start=linux.find(".fc") + 3
+            start=linux.find(".el") + 3
             fedora_version=linux[start:start+2]
         except Exception as e:
             print(f"Failed to get linux version:\n{e}")
@@ -371,7 +371,7 @@ def generate_changelog(
         if not fedora_version + "." in curr_pretty:
             curr_pretty=fedora_version + "." + curr_pretty
         pretty = target.capitalize()
-        pretty += " (F" + curr_pretty
+        pretty += " (CS" + curr_pretty
         if finish:
             pretty += ", #" + finish[:7]
         pretty += ")"