fix: authorize secure source branch deletion (Closes #1368)

src/main.py

@@ -497,6 +497,7 @@ class FollowingNotificationPayload(BaseModel):
 
 StepUpAction = Literal[
     "merge_pull",
+    "delete_source_branch",
     "submit_pull_review",
     "close_issue",
     "delete_comment",

src/request_boundary.py

@@ -8,7 +8,7 @@ API_MUTATION_BODY_LIMIT = 64 * 1024
 ISSUE_ATTACHMENT_BODY_LIMIT = 2 * 1024 * 1024 + 64 * 1024
 LEGACY_JSON_ATTACHMENT_BODY_LIMIT = 3 * 1024 * 1024
 UNFILED_DRAFT_SYNC_BODY_LIMIT = 17 * 1024 * 1024
-MUTATION_METHODS = frozenset({"POST", "PUT", "PATCH"})
+MUTATION_METHODS = frozenset({"POST", "PUT", "PATCH", "DELETE"})
 
 
 def request_body_limit(method: str, path: str) -> int | None: