github/workflows: Add workflows for all CI tasks, builds and tests.

Signed-off-by: Damien George <damien@micropython.org>

.github/workflows/ports_windows.yml

@@ -0,0 +1,23 @@
+name: windows port
+
+on:
+  push:
+  pull_request:
+    paths:
+      - '.github/workflows/*.yml'
+      - 'tools/**'
+      - 'py/**'
+      - 'extmod/**'
+      - 'lib/**'
+      - 'ports/unix/**'
+      - 'ports/windows/**'
+
+jobs:
+  build:
+    runs-on: ubuntu-latest
+    steps:
+    - uses: actions/checkout@v2
+    - name: Install packages
+      run: source tools/ci.sh && ci_windows_setup
+    - name: Build
+      run: source tools/ci.sh && ci_windows_build