Update Gradle version to "wrapper" in workflows

Author: programming-wolf

.github/workflows/build_main.yml

@@ -38,7 +38,7 @@ jobs:
       env:
         CI: true
       with:
-        gradle-version: 7.5.1
+        gradle-version: wrapper
         arguments: buildDocs
 
     # release and deploy only if we're building a release

.github/workflows/build_releasecandidate.yml

@@ -45,7 +45,7 @@ jobs:
         env:
           CI: true
         with:
-          gradle-version: 7.5.1
+          gradle-version: wrapper
           arguments: buildDocs
 
       # do the following two things only for a release!