Test support of external Python package platform dependencies

Although Arduino boards platforms traditionally have bundled all dependencies, there are some cases where the user will
need to use a preceeding workflow step to install external dependencies in the GitHub Actions runner environment.

Since it is a "composite action", the action supports this. The action uses a virtual environment for its own Python
package dependencies. This virtual environment might cause Python packages installed via the user's workflow (e.g., the
pyserial dependency of the ESP32 platform) to not be accessible to the compilation commands.

The added integration test will catch any regressions in the support for external Python package platform dependencies.

Author: per1234

.github/workflows/test-integration.yml

@@ -19,6 +19,7 @@ on:
 
 env:
   SKETCHES_REPORTS_PATH: sketches-reports
+  TESTDATA_PLATFORMS_PATH: .github/workflows/testdata/platforms
   TESTDATA_SKETCHES_PATH: .github/workflows/testdata/sketches
   TESTDATA_REPORTS_PATH:  .github/workflows/testdata/reports
 
@@ -203,6 +204,31 @@ jobs:
           sketch-paths: |
             - examples/Sweep
 
+  python-package-dependency:
+    runs-on: ubuntu-latest
+
+    steps:
+      - name: Checkout local repo
+        uses: actions/checkout@v3
+
+      - name: Install Python package dependency
+        run: pip install cowsay
+
+      - name: Run action with board that has external Python package dependency
+        # Use action from local path
+        uses: ./
+        with:
+          platforms: |
+            - name: arduino:avr
+            - source-path: ${{ env.TESTDATA_PLATFORMS_PATH }}/PythonPackageDependent
+              name: PythonPackageDependent:avr
+          fqbn: PythonPackageDependent:avr:package_dependent
+          libraries: |
+            []
+          sketch-paths: |
+            - ${{ env.TESTDATA_SKETCHES_PATH }}/BareMinimum
+
+
   check-sketches-reports:
     needs: all-inputs
     runs-on: ubuntu-latest

.github/workflows/testdata/platforms/PythonPackageDependent/boards.txt

@@ -0,0 +1,8 @@
+package_dependent.name=External Python Package Dependent Board
+package_dependent.upload.maximum_size=32256
+package_dependent.upload.maximum_data_size=2048
+package_dependent.build.mcu=atmega328p
+package_dependent.build.f_cpu=16000000L
+package_dependent.build.board=FOO
+package_dependent.build.core=arduino:arduino
+package_dependent.build.variant=arduino:standard

.github/workflows/testdata/platforms/PythonPackageDependent/dependent.py

@@ -0,0 +1,2 @@
+# Import external package to verify Python package dependencies can be installed by user into runner environment.
+import cowsay  # noqa: F401

.github/workflows/testdata/platforms/PythonPackageDependent/platform.txt

@@ -0,0 +1,3 @@
+name=External Python Package Dependent Platform
+version=0.0.0
+recipe.hooks.prebuild.1.pattern=python "{runtime.platform.path}/dependent.py"