Add shellcheck lint

Run shellcheck [1] on the bash files.

[1]: https://www.shellcheck.net/

Signed-off-by: Tim Crawford <tcrawford@system76.com>

.github/workflows/ci.yml

@@ -16,6 +16,9 @@ jobs:
       - name: Check formatting
         run: ./scripts/lint/02-clang-format.sh
 
+      - name: Check shell scripts
+        run: ./scripts/lint/03-shellcheck.sh
+
   tool:
     strategy:
       matrix: