[CI] backport upgrade to git-backporting@v4.8.0

* no-auto-squash: true so it DTRT for merged & squashed PRs
* target-branch-pattern: replaces the ad-hoc logic to determine the
  target branch name

It also now supports backporting to multiple branches. This is not
going to be immediately useful but will greatly help in three months
when there are two releases receiving backports.

.forgejo/workflows/backport.yml

@@ -45,39 +45,12 @@ jobs:
           cat <<'EOF'
           ${{ toJSON(github) }}
           EOF
-      - name: Fetch labels
+      - uses: https://code.forgejo.org/actions/git-backporting@v4.8.0
-        id: fetch-labels
-        shell: bash
-        run: |
-          set -x
-          echo "Labels retrieved below"
-          export DEBIAN_FRONTEND=noninteractive
-          apt-get update -qq
-          apt-get -q install -qq -y jq
-          filtered_labels=$(echo "$LABELS" | jq -c 'map(select(.name | startswith("backport/v")))')
-          echo "FILTERED_LABELS=${filtered_labels}" >> $GITHUB_ENV
-        env:
-          LABELS: ${{ toJSON(github.event.pull_request.labels) }}
-      - name: Extract targets
-        id: extract-targets
-        shell: bash
-        run: |
-          set -x
-          targets="$(echo $FILTERED_LABELS | jq -c '[.[] | .name | sub("backport/"; "")]')"
-          echo "targets=$(echo $targets)" >> $GITHUB_OUTPUT
-
-      - name: Printing info
-        shell: bash
-        run: |
-          echo "targets: ${{ steps.extract-targets.outputs.targets }}"
-          echo "target-branch: ${{ fromJSON(steps.extract-targets.outputs.targets)[0] }}"
-          echo "pull-request: ${{ github.event.pull_request.url }}"
-
-      - uses: https://code.forgejo.org/forgejo/git-backporting@b2554a678d5ea2814f0df3abad2ac4fcdee2d81f
         with:
-          target-branch: ${{ fromJSON(steps.extract-targets.outputs.targets)[0] }}/forgejo
+          target-branch-pattern: "^backport/(?<target>(v.*))$"
           strategy: ort
           strategy-option: find-renames
           cherry-pick-options: -x
           auth: ${{ secrets.BACKPORT_TOKEN }}
           pull-request: ${{ github.event.pull_request.url }}
+          auto-no-squash: true