CI: run only on file changes (#784)

.github/workflows/_test.yml

@@ -24,8 +24,13 @@ jobs:
     name: "test #${{ matrix.python-version }}"
     steps:
       - uses: actions/checkout@v4
-
+      - name: Get changed files
+        id: changed-files
+        uses: Ana06/get-changed-files@v2.2.0
+        with:
+          filter: "${{ inputs.working-directory }}/**"
       - name: Set up Python ${{ matrix.python-version }} + Poetry ${{ env.POETRY_VERSION }}
+        if: steps.changed-files.outputs.all
         uses: "./.github/actions/poetry_setup"
         with:
           python-version: ${{ matrix.python-version }}
@@ -34,17 +39,20 @@ jobs:
           cache-key: core
 
       - name: Install dependencies
+        if: steps.changed-files.outputs.all
         shell: bash
         working-directory: ${{ inputs.working-directory }}
         run: poetry install --with dev
 
       - name: Run core tests
+        if: steps.changed-files.outputs.all
         shell: bash
         working-directory: ${{ inputs.working-directory }}
         run: |
           make test
 
       - name: Ensure the tests did not create any additional files
+        if: steps.changed-files.outputs.all
         shell: bash
         working-directory: ${{ inputs.working-directory }}
         run: |