fix: pin griffe version and fix ExplanationStyle attribute error

Author: Sundar Raghavan

.github/workflows/breaking-change-check.yml

@@ -43,7 +43,7 @@ jobs:
           python-version: '3.10'
 
       - name: Install griffe
-        run: pip install griffe
+        run: pip install griffe==1.7.3
 
       # Fetch the base branch so the ref is available for griffe's worktree.
       - name: Fetch base branch
@@ -122,7 +122,7 @@ jobs:
               "",
           ]
           for b in breakages:
-              lines.append(b.explain(style=griffe.ExplanationStyle.markdown))
+              lines.append(b.explain())
 
           lines += [
               "",