Jenkins does not run the full test suite for tags

Originally created by @anonym on #17472 (Redmine)

When Jenkins tested the Tails 4.3 tag, it didn’t run @fragile scenarios, which is a bug. See e.g. https://jenkins.tails.boum.org/job/test_Tails_ISO_stable/2205/

In the console output I see this trace:

14:17:21 + echo origin/stable
14:17:21 + grep -q -E \+force-all-tests$
14:17:21 + [ stable = testing ]
14:17:21 + [ stable = feature/tor-nightly-master ]
14:17:21 + [ stable = devel ]
14:17:21 + git describe --tags --exact-match 4904a1fde8887488167a8a6c34b34c45b51aa112
14:17:21 + [ 4904a1fde8887488167a8a6c34b34c45b51aa112 != 4904a1fde8887488167a8a6c34b34c45b51aa112 ]
14:17:21 + TAGS_ARGS=--tag ~@fragile

for this part of wrap_test_suite:

if echo "${UPSTREAMJOB_GIT_BRANCH}" | grep -q -E '\+force-all-tests$' \
   || [ "${GIT_BRANCH#origin/}" = testing ] \
   || [ "${GIT_BRANCH#origin/}" = feature/tor-nightly-master ] \
   || [ "${GIT_BRANCH#origin/}" = devel ] ; then
    TAGS_ARGS=""
elif git describe --tags --exact-match "${UPSTREAMJOB_GIT_COMMIT}" >/dev/null 2>&1; then
    TAGS_ARGS=""
elif [ "${UPSTREAMJOB_GIT_COMMIT}" != "${UPSTREAMJOB_GIT_BASE_BRANCH_HEAD}" ] && \
       only_changes_doc "$UPSTREAMJOB_GIT_BASE_BRANCH_HEAD"; then
    TAGS_ARGS="--tag ~@fragile --tag @doc"
else
    TAGS_ARGS="--tag ~@fragile"
fi

So $UPSTREAMJOB_GIT_COMMIT is 4904a1fd, which is not the 4.3 tag (it is 2797053a), but just one of the commits I made yesterday, so the correct if-case for releases was not hit. Note that 4904a1fd is not the commit that was initially tagged 4.3 (FWIW, that was 4172c531), so there was no mix up with the tag update. I have no clue how 4904a1fd entered the picture since it doesn’t seem very special. Curious!