Bump org.mockito:mockito-bom from 5.20.0 to 5.21.0 (#300)

Bumps [org.mockito:mockito-bom](https://github.com/mockito/mockito) from 5.20.0 to 5.21.0.
- [Release notes](https://github.com/mockito/mockito/releases)
- [Commits](mockito/mockito@v5.20.0...v5.21.0)

---
updated-dependencies:
- dependency-name: org.mockito:mockito-bom
  dependency-version: 5.21.0
  dependency-type: direct:production
  update-type: version-update:semver-minor
...

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

Author: dependabot[bot]

build.gradle.kts

@@ -23,7 +23,7 @@ dependencies {
     testImplementation("org.junit.jupiter:junit-jupiter")
     testRuntimeOnly("org.junit.platform:junit-platform-launcher")  // gradle bundled version is incompatible with 5.12
 
-    testImplementation(platform("org.mockito:mockito-bom:5.20.0"))
+    testImplementation(platform("org.mockito:mockito-bom:5.21.0"))
     testImplementation("org.mockito:mockito-core")
 
     // util