build(deps): bump io.micrometer:micrometer-registry-prometheus

Bumps [io.micrometer:micrometer-registry-prometheus](https://github.com/micrometer-metrics/micrometer) from 1.13.5 to 1.13.6.
- [Release notes](https://github.com/micrometer-metrics/micrometer/releases)
- [Commits](micrometer-metrics/micrometer@v1.13.5...v1.13.6)

---
updated-dependencies:
- dependency-name: io.micrometer:micrometer-registry-prometheus
  dependency-type: direct:production
  update-type: version-update:semver-patch
...

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

backend/build.gradle.kts

@@ -54,7 +54,7 @@ dependencies {
     implementation("org.springframework.session:spring-session-core")
 
     implementation("io.micrometer:micrometer-core:1.13.5")
-    implementation("io.micrometer:micrometer-registry-prometheus:1.13.5")
+    implementation("io.micrometer:micrometer-registry-prometheus:1.13.6")
     implementation("net.ttddyy.observation:datasource-micrometer:1.0.5")
 
     implementation("io.swagger.core.v3:swagger-models:2.2.25")