build(deps): bump slf4j from 2.0.13 to 2.0.15

Bumps `slf4j` from 2.0.13 to 2.0.15.

Updates `org.slf4j:slf4j-api` from 2.0.13 to 2.0.15

Updates `org.slf4j:slf4j-nop` from 2.0.13 to 2.0.15

---
updated-dependencies:
- dependency-name: org.slf4j:slf4j-api
  dependency-type: direct:production
  update-type: version-update:semver-patch
- dependency-name: org.slf4j:slf4j-nop
  dependency-type: direct:production
  update-type: version-update:semver-patch
...

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

Author: dependabot[bot]

gradle/libs.versions.toml

@@ -7,7 +7,7 @@ spring-boot-v2 = "2.7.18"
 spring-boot-v3 = "3.2.1"
 openjdk-jmh = "1.36"
 ktor = "2.3.12"
-slf4j = "2.0.13"
+slf4j = "2.0.15"
 # https://kotlinlang.org/docs/ksp-quickstart.html
 # https://github.com/google/ksp
 ksp = "2.0.0-1.0.24"