Bump spotless-plugin-gradle from 5.14.2 to 6.1.2

Bumps spotless-plugin-gradle from 5.14.2 to 6.1.2.

---
updated-dependencies:
- dependency-name: com.diffplug.spotless:spotless-plugin-gradle
  dependency-type: direct:production
  update-type: version-update:semver-major
...
Signed-off-by: Ndependabot[bot] <support@github.com>

build.gradle

@@ -5,7 +5,7 @@ buildscript {
         }
     }
     dependencies {
-        classpath "com.diffplug.spotless:spotless-plugin-gradle:5.14.2"
+        classpath "com.diffplug.spotless:spotless-plugin-gradle:6.1.2"
         classpath "com.github.jxnu-liguobin:leetcode-helper:0.1.4"
     }
 }