ci(checks): trim matrix, ccache tests, modernize python_checks

Port the checks.yml and python_checks.yml improvements from the CI
orchestrator branch (mrpollo/ci_orchestration, PR #26257) without
doing the full T1/T2 split.

checks.yml:
- Drop 5 matrix entries the orchestrator removed:
  tests_coverage, px4_fmu-v2_default stack_check,
  NO_NINJA_BUILD=1 px4_fmu-v5_default,
  NO_NINJA_BUILD=1 px4_sitl_default, px4_sitl_allyes.
- Remove the codecov/codecov-action@v1 step (deprecated, only ran
  for the dropped tests_coverage entry).
- Wire the setup-ccache / save-ccache composite actions around
  make tests (cache-key-prefix ccache-sitl, max-size 300M) so
  repeat runs reuse the SITL build tree. Matches the orchestrator
  basic-tests job 1:1.

python_checks.yml:
- Replace the apt-get install python3 + pip install
  --break-system-packages + hardcoded $HOME/.local/bin paths with
  actions/setup-python@v5 pinned to 3.10 and plain pip install.
- Linters now run from PATH instead of $HOME/.local/bin.

Stacks on top of mrpollo/ci-checkout-hygiene (#27032) which shipped
fail-fast: true, fetch-depth: 1, and the safe.directory step
extraction.

Signed-off-by: Ramon Roche <mrpollo@gmail.com>

.github/workflows/python_checks.yml

@@ -20,14 +20,16 @@ jobs:
       with:
         fetch-depth: 1
 
-    - name: Install Python3
-      run: sudo apt-get install python3 python3-setuptools python3-pip -y
+    - name: Setup Python
+      uses: actions/setup-python@v5
+      with:
+        python-version: "3.10"
 
     - name: Install tools
-      run: python3 -m pip install mypy types-requests flake8 --break-system-packages
+      run: pip install mypy types-requests flake8
 
     - name: Check MAVSDK test scripts with mypy
-      run: $HOME/.local/bin/mypy --strict test/mavsdk_tests/*.py
+      run: mypy --strict test/mavsdk_tests/*.py
 
     - name: Check MAVSDK test scripts with flake8
-      run: $HOME/.local/bin/flake8 test/mavsdk_tests/*.py
+      run: flake8 test/mavsdk_tests/*.py