chore: add labeler action workflow

.github/labeler.yml

@@ -0,0 +1,23 @@
+# https://github.com/actions/labeler?tab=readme-ov-file#usage
+
+# Add the `4.8` label to PRs that target the `4.8` branch.
+'4.8': # @todo change value whenever the next minor version is changed
+- base-branch: '4.8'
+
+# Add the `github_actions` label to PRs that change any file in the `.github/workflows/` directory.
+'github_actions':
+- changed-files:
+  - any-glob-to-any-file:
+    - '.github/workflows/*'
+
+# Add the `documentation` label to PRs that change any file in the `user_guide_src/source/` directory.
+'documentation':
+- changed-files:
+  - any-glob-to-all-files:
+    - 'user_guide_src/source/*'
+
+# Add the `testing` label to PRs that change files in the `tests/` directory ONLY.
+'testing':
+- changed-files:
+  - any-glob-to-all-files:
+    - 'tests/*'

.github/workflows/label-pr.yml

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+name: Add Labels to PRs
+
+# NOTE: When updating this workflow, you should first change the event to `pull_request` to test the changes
+# in a PR, and then change it back to `pull_request_target` before merging.
+# @see https://github.com/actions/labeler?tab=readme-ov-file#updating-major-version-of-the-labeler
+on:
+  - pull_request_target
+
+jobs:
+  add-labels:
+    permissions:
+      contents: read
+      pull-requests: write
+    runs-on: ubuntu-24.04
+
+    steps:
+      - name: Add labels
+        uses: actions/labeler@634933edcd8ababfe52f92936142cc22ac488b1b # v6.0.1
+        with:
+          sync-labels: true # Remove labels when matching files are reverted