Merge pull request #30 from mhashizume/maint/main/pdk-conditional

(maint) Use null value with Puppet 7

Author: joshcooper

.github/workflows/unit_tests_with_released_puppet_gem.yaml

@@ -17,7 +17,7 @@ jobs:
         include:
           - puppet_version: '7'
             ruby: '2.7'
-            puppet_forge_token: ''
+            puppet_forge_token: ${{ null }}
           - puppet_version: '8'
             ruby: '3.1'
             puppet_forge_token: 'YES'