refactor(changelog): oldest_rev related logic

Author: bearomorphism

commitizen/changelog.py

@@ -355,8 +355,7 @@ def get_oldest_and_newest_rev(
     if not (newest_tag := rules.find_tag_for(tags, newest)):
         raise NoCommitsFoundError("Could not find a valid revision range.")
 
-    oldest_tag = None
-    oldest_tag_name = None
+    oldest_tag_name: str | None = None
     if oldest:
         if not (oldest_tag := rules.find_tag_for(tags, oldest)):
             raise NoCommitsFoundError("Could not find a valid revision range.")
@@ -368,17 +367,19 @@ def get_oldest_and_newest_rev(
     if not tags_range:
         raise NoCommitsFoundError("Could not find a valid revision range.")
 
-    oldest_rev = tags_range[-1].name
     newest_rev = newest_tag.name
 
     # Return None for oldest_rev if:
     # 1. The oldest tag is the last tag in the list and matches the requested oldest tag, or
     # 2. The oldest and newest tags are the same
-    if (
-        oldest_rev == tags[-1].name
-        and oldest_rev == oldest_tag_name
-        or oldest_rev == newest_rev
-    ):
-        return None, newest_rev
+    oldest_rev: str | None = (
+        None
+        if (
+            tags_range[-1].name == tags[-1].name
+            and tags_range[-1].name == oldest_tag_name
+            or tags_range[-1].name == newest_rev
+        )
+        else tags_range[-1].name
+    )
 
     return oldest_rev, newest_rev