Move pre-commit to its own workflow

Author: jepler

.github/workflows/build.yml

@@ -42,14 +42,11 @@ jobs:
       # (e.g. - apt-get: gettext, etc; pip: circuitpython-build-tools, requirements.txt; etc.)
       run: |
         source actions-ci/install.sh
-    - name: Pip install Sphinx, pre-commit
+    - name: Pip install Sphinx
       run: |
-        pip install --force-reinstall Sphinx sphinx-rtd-theme sphinx-autoapi pre-commit
+        pip install --force-reinstall Sphinx sphinx-rtd-theme sphinx-autoapi
     - name: Library version
       run: git describe --dirty --always --tags
-    - name: Pre-commit hooks
-      run: |
-        pre-commit run --all-files
     - name: Clone and build circuitpython unix port
       run: |
         set -e

.github/workflows/pre-commit.yml

@@ -0,0 +1,21 @@
+# SPDX-FileCopyrightText: Copyright (c) 2019 Anthony Sottile
+#
+# SPDX-License-Identifier: MIT
+
+name: pre-commit
+
+on: [pull_request, push]
+
+jobs:
+  pre-commit:
+    runs-on: ubuntu-20.04
+    steps:
+    - uses: actions/checkout@v1
+    - uses: actions/setup-python@v1
+    - name: set PY
+      run: echo >>$GITHUB_ENV "PY=$(python -c 'import hashlib, sys;print(hashlib.sha256(sys.version.encode()+sys.executable.encode()).hexdigest())')"
+    - uses: actions/cache@v1
+      with:
+        path: ~/.cache/pre-commit
+        key: pre-commit|${{ env.PY }}|${{ hashFiles('.pre-commit-config.yaml') }}
+    - uses: pre-commit/action@v1.1.0