Bump plugin-publish-plugin from 0.20.0 to 0.21.0

Bumps plugin-publish-plugin from 0.20.0 to 0.21.0.

---
updated-dependencies:
- dependency-name: com.gradle.publish:plugin-publish-plugin
  dependency-type: direct:production
  update-type: version-update:semver-minor
...

Signed-off-by: dependabot[bot] <support@github.com>

build.gradle

@@ -5,7 +5,7 @@ buildscript {
         }
     }
     dependencies {
-        classpath "com.gradle.publish:plugin-publish-plugin:0.20.0"
+        classpath "com.gradle.publish:plugin-publish-plugin:0.21.0"
 
         def pluginVersion = "6.4.1"
         classpath "io.freefair.gradle:maven-plugin:$pluginVersion"