Adapt workflow to use GitHub runners instead of self-hosted runners (#800)

Remove self-hosted runner configuration from the test workflow:
- Remove `self-hosted-runner: true` parameter
- Remove `self-hosted-runner-label: edge` parameter

The workflow now uses GitHub-hosted runners with the default `runs-on-base: ubuntu-24.04` configuration.

Author: seb4stien

.github/workflows/test.yaml

@@ -11,6 +11,4 @@ jobs:
     uses: canonical/operator-workflows/.github/workflows/test.yaml@main
     secrets: inherit
     with:
-      self-hosted-runner: true
-      self-hosted-runner-label: edge
       vale-style-check: false