build(deps): bump dev.langchain4j:langchain4j-community-bom

Bumps [dev.langchain4j:langchain4j-community-bom](https://github.com/langchain4j/langchain4j-community) from 1.11.0-beta19 to 1.12.1-beta21.
- [Release notes](https://github.com/langchain4j/langchain4j-community/releases)
- [Commits](langchain4j/langchain4j-community@1.11.0-beta19...1.12.1-beta21)

---
updated-dependencies:
- dependency-name: dev.langchain4j:langchain4j-community-bom
  dependency-version: 1.12.1-beta21
  dependency-type: direct:production
  update-type: version-update:semver-minor
...

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

Author: dependabot[bot]

platform/build.gradle

@@ -25,7 +25,7 @@ dependencies {
     def jacksonAnnotationsVersion = "2.21"
     def jugVersion = "5.2.0"
     def langchain4jVersion = "1.11.0"
-    def langchain4jCommunityVersion = "1.11.0-beta19"
+    def langchain4jCommunityVersion = "1.12.1-beta21"
     def jettyVersion = "12.0.31" // Wiremock uses an older version as Micronaut
 
     // as Jackson is in the Micronaut BOM, to force its version we need to use enforcedPlatform but it didn't really work, see later :(