Bump com.squareup.okhttp3:okhttp-bom in /samples/java

Bumps [com.squareup.okhttp3:okhttp-bom](https://github.com/square/okhttp) from 5.1.0 to 5.2.1.
- [Changelog](https://github.com/square/okhttp/blob/master/CHANGELOG.md)
- [Commits](square/okhttp@parent-5.1.0...parent-5.2.1)

---
updated-dependencies:
- dependency-name: com.squareup.okhttp3:okhttp-bom
  dependency-version: 5.2.1
  dependency-type: direct:production
  update-type: version-update:semver-minor
...

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

Author: dependabot[bot]

samples/java/build.gradle.kts

@@ -8,7 +8,7 @@ repositories {
 }
 
 dependencies {
-    implementation(platform("com.squareup.okhttp3:okhttp-bom:5.1.0"))
+    implementation(platform("com.squareup.okhttp3:okhttp-bom:5.2.1"))
     implementation("com.squareup.okhttp3:okhttp")
     implementation("com.squareup.okhttp3:okhttp-sse")
     implementation(platform("com.fasterxml.jackson:jackson-bom:2.20.0"))