deps: bump com.github.spotbugs from 6.0.20 to 6.0.21 (#171)

Bumps com.github.spotbugs from 6.0.20 to 6.0.21.

---
updated-dependencies:
- dependency-name: com.github.spotbugs
  dependency-type: direct:production
  update-type: version-update:semver-patch
...

Signed-off-by: dependabot[bot] <[email protected]>
Co-authored-by: dependabot[bot] <49699333+dependabot[bot]@users.noreply.github.com>

build.gradle

@@ -3,7 +3,7 @@ import java.text.SimpleDateFormat
 
 plugins {
     id 'checkstyle'
-    id "com.github.spotbugs" version "6.0.20"
+    id "com.github.spotbugs" version "6.0.21"
     id 'io.github.goooler.shadow' version '8.1.8'
     id 'java'
 }