[llvm][github] Allow `/` in branches name in the `/branch` command

[cor3ntin]

Summary

IE cor3ntin/llvm-project/cor3ntin/foo

[aaron.ballman]

FWIW, I ran into this today with an attempt to backport https://github.com/llvm/llvm-project/issues/64713, so I'm in favor of the changes. It'd also be nice if we could silently accept // cherry-pick: and // branch: (with a colon) because I managed to mess that up as well. :-D

[cor3ntin]

After thinking about it, I don't think this fix make sense.
foo/bar:foo/bar should be a valid refspec.
I also validated that the /branch regex seem correct. So... not sure what the issue is. Sorry for creating that too quick!

llvm/utils/git/github-automation.py

class ReleaseWorkflow:
     def check_if_pull_request_exists(
         self, repo: github.Repository.Repository, head: str
     ) -> bool:
         pulls = repo.get_pulls(head=head)
         return pulls.totalCount != 0
 
     def create_pull_request(self, owner: str, repo_name: str, branch: str) -> bool:
         """
-        reate a pull request in `self.branch_repo_name`.  The base branch of the
+        Create a pull request in `self.branch_repo_name`.  The base branch of the
         pull request will be chosen based on the the milestone attached to
         the issue represented by `self.issue_number`  For example if the milestone
         is Release 13.0.1, then the base branch will be release/13.x. `branch`
         will be used as the compare branch.
         https://docs.github.com/en/get-started/quickstart/github-glossary#base-branch
         https://docs.github.com/en/get-started/quickstart/github-glossary#compare-branch
         """
         repo = github.Github(self.token).get_repo(self.branch_repo_name)
         issue_ref = "{}#{}".format(self.repo_name, self.issue_number)
         pull = None
         release_branch_for_issue = self.release_branch_for_issue
         if release_branch_for_issue is None:
             return False
-        head_branch = branch
+        local_name = branch.replace("/", "_")
+        head_branch = local_name
         if not repo.fork:
             # If the target repo is not a fork of llvm-project, we need to copy
             # the branch into the target repo.  GitHub only supports cross-repo pull
             # requests on forked repos.
             head_branch = f"{owner}-{branch}"
             local_repo = Repo(self.llvm_project_dir)
             push_done = False
             for _ in range(0, 5):
                 try:
                     local_repo.git.fetch(
-                        f"https://github.com/{owner}/{repo_name}", f"{branch}:{branch}"
+                        f"https://github.com/{owner}/{repo_name}", f"{branch}:{local_name}"
                     )
                     local_repo.git.push(
-                        self.push_url, f"{branch}:{head_branch}", force=True
+                        self.push_url, f"{local_name}:{head_branch}", force=True
                     )
                     push_done = True
                     break
                 except Exception as e:
                     print(e)
                     time.sleep(30)
                     continue
             if not push_done: