fix(ci): fine tune the testing matrix

- run the qa tools only once
- test only one combination of isort/flake8 with all python versions
- the whole matrix of isort/flake8 versions only with python 3.9

Author: gforcada

.github/workflows/tests.yml

@@ -8,13 +8,31 @@ env:
   GITHUB_TOKEN: ${{ secrets.GITHUB_TOKEN }}
 jobs:
   test:
-    name: Python ${{ matrix.python-version }} x isort ${{ matrix.isort }} x flake8 ${{ matrix.flake8 }}
+    name: py-${{ matrix.python-version }}/isort-${{ matrix.isort }}/flake8-${{ matrix.flake8 }}
     runs-on: ubuntu-latest
     strategy:
       matrix:
         python-version: ["3.10", 3.9, 3.8, 3.7, pypy-3.9]
-        isort: [4.3.21, 5.10.1]
-        flake8: [3.9.2, 4.0.1, 5.0.4]
+        isort: [5.10.1]
+        flake8: [5.0.4]
+        include:
+          - python-version: 3.9
+            isort: 5.10.1
+            flake8: 4.0.1
+            qa: 'true'
+          - python-version: 3.9
+            isort: 5.10.1
+            flake8: 3.9.2
+
+          - python-version: 3.9
+            isort: 4.3.21
+            flake8: 5.0.4
+          - python-version: 3.9
+            isort: 4.3.21
+            flake8: 4.0.1
+          - python-version: 3.9
+            isort: 4.3.21
+            flake8: 3.9.2
     steps:
       - uses: actions/checkout@v3
       - name: Set up Python
@@ -40,31 +58,31 @@ jobs:
         if: matrix.isort == '4.3.21'
       # formatters
       - name: Run pyupgrade
-        if: matrix.python-version == '3.9'
+        if: matrix.qa == 'true'
         run: pyupgrade --py37-plus *.py
       - name: Run isort
-        if: matrix.python-version == '3.9'
+        if: matrix.qa == 'true'
         run: isort --check-only *.py
       - name: Run black
-        if: matrix.python-version == '3.9'
+        if: matrix.qa == 'true'
         run: black --check --skip-string-normalization *.py
       # linters
       - name: Lint with bandit
-        if: matrix.python-version == '3.9'
+        if: matrix.qa == 'true'
         run: bandit --skip B101 *.py  # B101 is assert statements
       - name: Lint with codespell
-        if: matrix.python-version == '3.9'
+        if: matrix.qa == 'true'
         run: codespell *.rst *.py
       - name: Lint with flake8
-        if: matrix.python-version == '3.9'
+        if: matrix.qa == 'true'
         run: flake8 *.py --count --max-complexity=18 --max-line-length=88 --show-source --statistics
       - name: Lint with mypy
-        if: matrix.python-version == '3.9'
+        if: matrix.qa == 'true'
         run: |
           mkdir --parents --verbose .mypy_cache
           mypy --ignore-missing-imports --install-types --non-interactive *.py || true
       - name: Lint with safety
-        if: matrix.python-version == '3.9'
+        if: matrix.qa == 'true'
         run: safety check  || true
       # tests and coverage
       - name: Test