[PULP-809] Update shell script to comply with shellcheck

[pedro-psb]

Addressing mainly this:

/usr/lib/python3.12/site-packages/pulp_rpm/tests/functional/sign-metadata.sh:15:74: warning[[SC1083](https://github.com/koalaman/shellcheck/wiki/SC1083)]: This } is literal. Check expression (missing ;/\n?) or quote it.
#   13|   STATUS=$?
#   14|   if [[ ${STATUS} -eq 0 ]]; then
#   15|->    echo {\"file\": \"${FILE_PATH}\", \"signature\": \"${SIGNATURE_PATH}\"}
#   16|   else
#   17|      exit ${STATUS}

[patchback]

Backport to 3.26: 💚 backport PR created

✅ Backport PR branch: patchback/backports/3.26/1282d25420960281c01025cd35b9862a8b450865/pr-4262

Backported as #4263

🤖 @patchback
I'm built with octomachinery and
my source is open — https://github.com/sanitizers/patchback-github-app.

[patchback]

Backport to 3.29: 💚 backport PR created

✅ Backport PR branch: patchback/backports/3.29/1282d25420960281c01025cd35b9862a8b450865/pr-4262

Backported as #4264

🤖 @patchback
I'm built with octomachinery and
my source is open — https://github.com/sanitizers/patchback-github-app.

[patchback]

Backport to 3.27: 💚 backport PR created

✅ Backport PR branch: patchback/backports/3.27/1282d25420960281c01025cd35b9862a8b450865/pr-4262

Backported as #4265

🤖 @patchback
I'm built with octomachinery and
my source is open — https://github.com/sanitizers/patchback-github-app.

[patchback]

Backport to 3.34: 💚 backport PR created

✅ Backport PR branch: patchback/backports/3.34/1282d25420960281c01025cd35b9862a8b450865/pr-4262

Backported as #4266

🤖 @patchback
I'm built with octomachinery and
my source is open — https://github.com/sanitizers/patchback-github-app.