feat(ci): add branch input to Testing Farm workflow (podman-desktop#18396)

Signed-off-by: Anton Misskii <amisskii@redhat.com>
Co-authored-by: Claude Opus 4.6 (1M context) <noreply@anthropic.com>

Author: amisskii

.github/workflows/e2e-main-tf.yaml

@@ -31,6 +31,11 @@ on:
         description: 'TMT plan target to run (e.g. smoke, e2e, kubernetes, all)'
         type: string
         default: 'e2e'
+      branch:
+        default: 'main'
+        description: 'Podman Desktop repo branch'
+        type: string
+        required: false
 
 permissions:
   contents: read
@@ -63,6 +68,7 @@ jobs:
         uses: sclorg/testing-farm-as-github-action@230555baceb860aa468d216f1822974836b965d1
         with:
           api_key: ${{ secrets.TF_TOKEN }}
+          git_ref: ${{ github.event.inputs.branch || github.ref_name }}
           create_github_summary: "false"
           compose: ${{ matrix.fedora-version }}
           tmt_plan_filter: 'name:/tests/tmt/plans/pd-e2e-plan/${{ env.NPM_TARGET }}'