ci: revert to MegaLinter v6 GitHub action

cljstyle linter currently has an issue in v7
oxsecurity/megalinter#2716

Author: practicalli-johnny

.github/workflows/megalinter.yaml

@@ -38,7 +38,7 @@ jobs:
       - name: MegaLinter Run
         id: ml
         ## latest release of major version
-        uses: oxsecurity/megalinter/flavors/java@v7
+        uses: oxsecurity/megalinter/flavors/java@v6
         env:
           # ADD CUSTOM ENV VARIABLES OR DEFINE IN MEGALINTER_CONFIG file
           MEGALINTER_CONFIG: .github/config/megalinter.yaml