Bump io.openapiprocessor:build-plugins from 2025.4-SNAPSHOT to 2025.6

Bumps io.openapiprocessor:build-plugins from 2025.4-SNAPSHOT to 2025.6.

---
updated-dependencies:
- dependency-name: io.openapiprocessor:build-plugins
  dependency-version: '2025.6'
  dependency-type: direct:production
...

Signed-off-by: dependabot[bot] <support@github.com>

Author: dependabot[bot]

gradle/libs.versions.toml

@@ -3,7 +3,7 @@ openapiparser = "2025.4-SNAPSHOT"
 
 build-jdk = "11"
 test-jdk = "17"
-build-plugins = "2025.4-SNAPSHOT"
+build-plugins = "2025.6"
 
 # using the embedded kotlin version of gradle to avoid mixed versions
 kotlin = "2.2.10"