add gpg package to build - ubuntu-22.04 python 3.13 skips pgp tests.

The 3.13 tests on ubuntu-22.04 report that PGP tests are skipped
because:


  SKIPPED [1] test/test_mailgw.py:296: Skipping PGP tests: 'gpg' not installed


the same tests pass under python 3.12 and ubuntu-22.04. Under both
versions, the gpg build and install report no issues.

Add the gpg package to see if it fixes it.

(Log used:
https://github.com/roundup-tracker/roundup/actions/runs/11633664792/job/32399246320)

Author: rouilj

.github/workflows/ci-test.yml

@@ -223,7 +223,7 @@ jobs:
 
       - name: Install auxiliary packages
         run: |
-          sudo apt-get install swig gpgsm libgpgme-dev
+          sudo apt-get install swig gpg gpgsm libgpgme-dev
           # pygments for markdown2 to highlight code blocks
           pip install markdown2 pygments
           # docutils for ReStructuredText