Add GitHub action to build the environment with Guix.

Author: zimoun

.github/workflows/build.yml

@@ -0,0 +1,29 @@
+name: build
+on: [ push ]
+jobs:
+  build:
+    name: Run the pipeline
+    runs-on: ubuntu-22.04
+    steps:
+      - name: Guix cache
+        uses: actions/cache@v2
+        with:
+          path: ~/.cache/guix
+          # use a key that (almost) never matches
+          key: guix-cache-${{ github.sha }}
+          restore-keys: |
+            guix-cache-
+      - name: Install Guix
+        uses: PromyLOPh/guix-install-action@v1
+      - name: Checkout
+        uses: actions/checkout@v2
+      - name: Instantiate specific Guix revision
+        run: guix time-machine -C sources/channels.scm -- describe
+      - name: Check
+        run: guix time-machine -C sources/channels.scm -- describe
+      - name: Build environment
+        working-directory: sources
+        run: guix time-machine -C channels.scm -- shell -C -m manifest.scm -- python3 --version
+      - name: Rebuild environment for checking
+        working-directory: sources
+        run: guix time-machine -C channels.scm -- shell -C -m manifest.scm -- python3 --version