.github/charm: set tag prefix to 'error-tracker'

Author: Hyask

.github/workflows/build-and-test-charm.yaml

@@ -98,6 +98,6 @@ jobs:
         with:
           credentials: '${{ secrets.CHARMHUB_TOKEN }}'
           github-token: '${{ secrets.GITHUB_TOKEN }}'
-          tag-prefix: ${{ matrix.charm }}
+          tag-prefix: error-tracker
           built-charm-path: error-tracker_ubuntu@24.04-amd64.charm
         if: github.ref == 'refs/heads/main'