Bump org.mockito:mockito-core from 5.12.0 to 5.13.0

Bumps [org.mockito:mockito-core](https://github.com/mockito/mockito) from 5.12.0 to 5.13.0.
- [Release notes](https://github.com/mockito/mockito/releases)
- [Commits](mockito/mockito@v5.12.0...v5.13.0)

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

Signed-off-by: dependabot[bot] <[email protected]>

divviup/build.gradle.kts

@@ -59,7 +59,7 @@ dependencies {
     testImplementation("ch.qos.logback:logback-core:1.5.7")
     testImplementation("ch.qos.logback:logback-classic:1.5.7")
     testImplementation("commons-io:commons-io:2.16.1")
-    testImplementation("org.mockito:mockito-core:5.12.0")
+    testImplementation("org.mockito:mockito-core:5.13.0")
     androidTestImplementation(project(":divviup:commontest"))
     androidTestImplementation("androidx.test.ext:junit:1.2.1")
     androidTestImplementation("androidx.test.espresso:espresso-core:3.6.1")