Pushing tags doesn't work

[sdruskat]

Copying the GitHub template and changing it to run on pushed tags leads to a failing workflow:

on:
  push:
    tags:
      - "**"

This is because the checkout actions (or rather, git) checks out into detached HEAD state.

In these cases, a new branch must be created from the detached HEAD before copying it, otherwise you run into fatal: cannot copy the current branch while not on any.

We need to reflect this in the template and the docs website (docs.smp) as this is a very common case.

[sdruskat]

Action log:

Run # Cache current branch for PR close job
  # Cache current branch for PR close job
  git branch --show-current > .hermes/curate/target_branch
  
  # Shorten the SHA for the PR title
  SHORT_SHA=$(echo "$GITHUB_SHA" | cut -c -8)
  echo "SHORT_SHA=$SHORT_SHA" >> "$GITHUB_ENV"
  
  # Create a curation branch
  git branch -c "hermes/curate-$SHORT_SHA"                                   <--- Fails!
  git push origin "hermes/curate-$SHORT_SHA"
  
  # Explicitly add to-be-curated metadata (which is ignored via .gitignore!)
  git add -f .hermes/curate
  shell: /usr/bin/bash -e {0}
  env:
    pythonLocation: /opt/hostedtoolcache/Python/3.10.15/x64
    PKG_CONFIG_PATH: /opt/hostedtoolcache/Python/3.10.15/x64/lib/pkgconfig
    Python_ROOT_DIR: /opt/hostedtoolcache/Python/3.10.15/x64
    Python2_ROOT_DIR: /opt/hostedtoolcache/Python/3.10.15/x64
    Python3_ROOT_DIR: /opt/hostedtoolcache/Python/3.10.15/x64
    LD_LIBRARY_PATH: /opt/hostedtoolcache/Python/3.10.15/x64/lib
fatal: cannot copy the current branch while not on any
Error: Process completed with exit code 128.

[sdruskat]

One workaround could be something like

# If HEAD is detached (e.g., when a tag has been checked out),
# switch to new temporary branch hermes/tmp/<current ref>,
# and push that to origin
if [ $(git branch --show-current | wc -l) -eq "0" ]; then
  HERMES_TMP_BRANCH=hermes/tmp-$(git rev-parse --short HEAD)
  git switch -c $HERMES_TMP_BRANCH
  git push -u origin $HERMES_TMP_BRANCH
fi

Then, the branch should also be deleted in hermes-curate and hermes-cleanup:

for BRANCH in $(git ls-remote origin 'refs/heads/hermes/curate-*' | cut -f2 | cut -d'/' -f'3-'); do
  git push origin --delete "$BRANCH"
done
for BRANCH in $(git ls-remote origin 'refs/heads/$HERMES_TMP_BRANCH' | cut -f2 | cut -d'/' -f'3-'); do   <---
  git push origin --delete "$BRANCH"                                                                     <---
done                                                                                                     <---