Add shell-check job

We don't want to fail on shellcheck yet.

.github/workflows/test.yml

@@ -25,6 +25,27 @@ jobs:
       - uses: actions/setup-python@v2
       - uses: pre-commit/action@v2.0.3
 
+  check-shell:
+    runs-on: ubuntu-latest
+    steps:
+      - uses: actions/checkout@v2
+      - uses: actions/setup-python@v2
+      - run: |
+          python -m venv venv && source venv/bin/activate
+          pip install gh-release-install
+
+          sudo venv/bin/gh-release-install \
+            koalaman/shellcheck \
+            shellcheck-{tag}.linux.x86_64.tar.xz --extract shellcheck-{tag}/shellcheck \
+            /usr/bin/shellcheck
+
+          sudo venv/bin/gh-release-install \
+            mvdan/sh \
+            shfmt_{tag}_linux_amd64 \
+            /usr/bin/shfmt
+
+      - run: make shell-check
+
   test:
     strategy:
       matrix:

Makefile

@@ -13,4 +13,4 @@ shell-format:
 
 shell-check:
 	shfmt -f . | xargs shfmt -i 2 -ci -sr -kp -d
-	shfmt -f . | xargs shellcheck --color=always
+	shfmt -f . | xargs shellcheck --color=always || true