chore(deps): bump pl.allegro.tech.build.axion-release in /backend

Bumps [pl.allegro.tech.build.axion-release](https://github.com/allegro/axion-release-plugin) from 1.18.14 to 1.18.15.
- [Release notes](https://github.com/allegro/axion-release-plugin/releases)
- [Commits](allegro/axion-release-plugin@v1.18.14...v1.18.15)

---
updated-dependencies:
- dependency-name: pl.allegro.tech.build.axion-release
  dependency-type: direct:production
  update-type: version-update:semver-patch
...

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

Author: dependabot[bot]

backend/build.gradle

@@ -22,7 +22,7 @@
  * SOFTWARE.
  */
 plugins {
-    id "pl.allegro.tech.build.axion-release" version "1.18.14"
+    id "pl.allegro.tech.build.axion-release" version "1.18.15"
     id "com.diffplug.spotless" version "6.25.0"
     id "org.jetbrains.kotlin.jvm" version "2.0.21"
     id "org.jetbrains.kotlin.plugin.allopen" version "2.0.21"