Add shellcheck target

.github/workflows/shellcheck.yml

@@ -8,7 +8,7 @@ jobs:
     steps:
       - uses: actions/checkout@v3
       - uses: ludeeus/action-shellcheck@master
-      - run: ./bin/run-shellcheck
+      - run: make shellcheck
 on:
   push:
     branches: [ main ]

Makefile

@@ -13,3 +13,7 @@ deinstall:
 	rm -rf $(LIBEXECDIR)
 	rm -f $(BINDIR)/portzap
 	rm -f $(MANDIR)/portzap.8
+
+shellcheck:
+	shellcheck bin/portzap
+	shellcheck libexec/portzap/*