update linting workflow to not run multiple times unnecessarily

.github/workflows/linting.yml

@@ -3,19 +3,42 @@ name: Linting
 on: [push,pull_request]
 
 jobs:
-  flake8_py3:
+  precheck:
-    runs-on: ubuntu-latest
+    runs-on: ubuntu-20.04
+
+    outputs:
+      should_skip: ${{ steps.skip_check.outputs.should_skip }}
+    steps:
+      - id: skip_check
+        uses: fkirc/skip-duplicate-actions@master
+        with:
+          # skip concurrent jobs if they are on the same thing
+          concurrent_skipping: 'same_content'
+          # never skip PR + manual/scheduled runs
+          do_not_skip: '["pull_request", "workflow_dispatch", "schedule"]'
+
+  flake8:
+    needs: precheck
+    if: ${{ needs.precheck.outputs.should_skip != 'true' }}
+    runs-on: ubuntu-20.04
+
+    strategy:
+      matrix:
+        python-version: [3.9]
+
     steps:
       - uses: actions/checkout@master
-      - uses: actions/setup-python@v1
+      - name: Setup Python ${{ matrix.python-version }}
+        uses: actions/setup-python@v1
         with:
-          python-version: 3.9
+          python-version: ${{ matrix.python-version }}
           architecture: x64
       - name: Install flake8
         run: pip install flake8
       - name: Run flake8
         uses: suo/flake8-github-action@releases/v1
         with:
-          checkName: 'flake8_py3'   # NOTE: this needs to be the same as the job name
+          checkName: 'flake8'   # NOTE: this needs to be the same as the job name
         env:
           GITHUB_TOKEN: ${{ secrets.GITHUB_TOKEN }}
+