tests: validate developer bash commands

Also change the logic a bit to iterate over the individual files per
directory, as having a directory without bash commands will otherwise
pass a literal `*.sh` to `bash -n`, causing it to fail.

Closes Homebrew/homebrew#48323.

Signed-off-by: Martin Afanasjew <martin@afanasjew.de>

Library/Homebrew/test/test_bash.rb

@@ -11,6 +11,10 @@ class BashTests < Homebrew::TestCase
   end
 
   def test_bash_cmds
-    assert_valid_bash_syntax "#{HOMEBREW_LIBRARY_PATH}/cmd/*.sh"
+    %w[cmd dev-cmd].each do |dir|
+      Dir["#{HOMEBREW_LIBRARY_PATH}/#{dir}/*.sh"].each do |cmd|
+        assert_valid_bash_syntax cmd
+      end
+    end
   end
 end