ci: fetch tags before publishing

The tags affect the name of the built artefact AND are required for the
check below. Otherwise not versions get pushed to PyPI.

See: #536

.builds/archlinux.yml

@@ -32,6 +32,7 @@ tasks:
       codecov
   - package: |
       cd todoman
+      git fetch --tags
       python -m build --no-isolation
       git describe --exact-match --tags || complete-build
   - publish: |