Editor copy build failures when branch name includes a `/`

[LPardue]

I have a tendency to use a / in branch names as a convention. For example lucas/fix-spelling-mistakes. In the http-extensions repo, this seems to trigger benign warnings in the editor copy build job.

See for example https://github.com/httpwg/http-extensions/actions/runs/17163156955/job/48697120546

Run martinthomson/i-d-template@v1
  with:
    make: gh-pages
    token: ***
/usr/bin/docker run --name ghcriomartinthomsonidtemplateactionlatest_8f210d --label 30745e --workdir /github/workspace --rm -e "INPUT_MAKE" -e "INPUT_TOKEN" -e "GITHUB_TOKEN" -e "HOME" -e "GITHUB_JOB" -e "GITHUB_REF" -e "GITHUB_SHA" -e "GITHUB_REPOSITORY" -e "GITHUB_REPOSITORY_OWNER" -e "GITHUB_REPOSITORY_OWNER_ID" -e "GITHUB_RUN_ID" -e "GITHUB_RUN_NUMBER" -e "GITHUB_RETENTION_DAYS" -e "GITHUB_RUN_ATTEMPT" -e "GITHUB_ACTOR_ID" -e "GITHUB_ACTOR" -e "GITHUB_WORKFLOW" -e "GITHUB_HEAD_REF" -e "GITHUB_BASE_REF" -e "GITHUB_EVENT_NAME" -e "GITHUB_SERVER_URL" -e "GITHUB_API_URL" -e "GITHUB_GRAPHQL_URL" -e "GITHUB_REF_NAME" -e "GITHUB_REF_PROTECTED" -e "GITHUB_REF_TYPE" -e "GITHUB_WORKFLOW_REF" -e "GITHUB_WORKFLOW_SHA" -e "GITHUB_REPOSITORY_ID" -e "GITHUB_TRIGGERING_ACTOR" -e "GITHUB_WORKSPACE" -e "GITHUB_ACTION" -e "GITHUB_EVENT_PATH" -e "GITHUB_ACTION_REPOSITORY" -e "GITHUB_ACTION_REF" -e "GITHUB_PATH" -e "GITHUB_ENV" -e "GITHUB_STEP_SUMMARY" -e "GITHUB_STATE" -e "GITHUB_OUTPUT" -e "RUNNER_OS" -e "RUNNER_ARCH" -e "RUNNER_NAME" -e "RUNNER_ENVIRONMENT" -e "RUNNER_TOOL_CACHE" -e "RUNNER_TEMP" -e "RUNNER_WORKSPACE" -e "ACTIONS_RUNTIME_URL" -e "ACTIONS_RUNTIME_TOKEN" -e "ACTIONS_CACHE_URL" -e "ACTIONS_RESULTS_URL" -e GITHUB_ACTIONS=true -e CI=true -v "/var/run/docker.sock":"/var/run/docker.sock" -v "/home/runner/work/_temp/_github_home":"/github/home" -v "/home/runner/work/_temp/_github_workflow":"/github/workflow" -v "/home/runner/work/_temp/_runner_file_commands":"/github/file_commands" -v "/home/runner/work/http-extensions/http-extensions":"/github/workspace" ghcr.io/martinthomson/i-d-template-action:latest  "gh-pages"
warning: lib/default-branch.py: correcting the default branch locally:
warning: lib/default-branch.py:     git symbolic-ref refs/remotes/origin/HEAD refs/remotes/origin/main
make: '.targets.mk' is up to date.
warning: lib/default-branch.py: correcting the default branch locally:
warning: lib/default-branch.py:     git symbolic-ref refs/remotes/origin/HEAD refs/remotes/origin/main
git fetch -qf origin gh-pages:gh-pages
git clone -q -b gh-pages . /tmp/ghpages61
git fetch -qf origin gh-pages:gh-pages
git clone -q -b gh-pages . /tmp/ghpages121
mkdir -p /tmp/ghpages121/lucas/fix-3183
Remove obsolete 'draft-ietf-httpbis-optimistic-upgrade-05'
Remove obsolete 'lucas'
fatal: pathspec 'lucas' did not match any files
make[1]: *** [lib/ghpages.mk:90: cleanup-ghpages] Error 128
make[1]: Target 'ghpages' not remade because of errors.
make: *** [lib/ghpages.mk:131: ghpages] Error 2

On merge to main, the problem vanishes (which is expected)