Ignore suggestion to follow source includes.

These are typically not easy to hardcode, nor do they contain
much actual shell code, so let's just ignore.

Author: eldering

.github/workflows/shellcheck.yml

@@ -16,3 +16,5 @@ jobs:
       - uses: actions/checkout@v2
       - name: Run ShellCheck
         uses: ludeeus/action-shellcheck@master
+        env:
+          SHELLCHECK_OPTS: -e SC1090