workflows: skip basic test for docs

The basic test workflow is skipped for changes only in the docs
directory. Because this workflow is required, basic_test_skipped.yaml
is added to run in its absence and provide a successful completion.

.github/workflows/basic_test.yaml

@@ -3,14 +3,22 @@
 # pyocd workflow for:
 # - checking code with flake8
 # - running unit tests
+# - run test/import_all.py script
+# - build source distro and wheel, check with twine
 
 name: basic test
 
-on: [push, pull_request]
+# Don't run for changes that only affect the docs directory.
+on:
+  push:
+    paths-ignore:
+      - 'docs/**'
+  pull_request:
+    paths-ignore:
+      - 'docs/**'
 
 jobs:
   build:
-
     runs-on: ${{ matrix.os }}
     strategy:
       matrix:

.github/workflows/basic_test_skipped.yaml

@@ -0,0 +1,19 @@
+# Copyright (c) 2021-2022 Chris Reed
+
+# pyocd workflow to fill in for the skipped 'basic test' workflow for docs updates. Without this,
+# the required 'basic test' workflow will not have run and therefore docs PRs won't be mergeable.
+#
+# See this documentation for more about the need for this workaround: https://docs.github.com/en/repositories/configuring-branches-and-merges-in-your-repository/defining-the-mergeability-of-pull-requests/troubleshooting-required-status-checks#handling-skipped-but-required-checks
+
+name: basic test
+
+on:
+  pull_request:
+    paths:
+      - 'docs/**'
+
+jobs:
+  build:
+    runs-on: ubuntu-latest
+    steps:
+      - run: 'echo "Skipped due to path filter."'