Disable ARM integration tests (#490)

Too high cost on GitHub-hosted ARM runners

Will try to re-enable on nightly only if costs are low enough, but disabling all for now so that new PR runs do not create further costs

Author: carlcsaposs-canonical

.github/workflows/ci.yaml

@@ -58,7 +58,6 @@ jobs:
             allure_on_amd64: true
         architecture:
           - amd64
-          - arm64
     name: Integration test charm | ${{ matrix.juju.agent }} | ${{ matrix.architecture }}
     needs:
       - lint