[Tech] Bump org.flywaydb:flyway-database-postgresql in /backend

Bumps org.flywaydb:flyway-database-postgresql from 10.21.0 to 11.3.0.

---
updated-dependencies:
- dependency-name: org.flywaydb:flyway-database-postgresql
  dependency-type: direct:production
  update-type: version-update:semver-major
...

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

backend/build.gradle.kts

@@ -55,7 +55,7 @@ dependencies {
     implementation("org.n52.jackson:jackson-datatype-jts:1.2.10")
     implementation("com.nhaarman.mockitokotlin2:mockito-kotlin:2.2.0")
     implementation("org.flywaydb:flyway-core:11.1.0")
-    implementation("org.flywaydb:flyway-database-postgresql:10.21.0")
+    implementation("org.flywaydb:flyway-database-postgresql:11.3.0")
     implementation("org.jetbrains.kotlin:kotlin-reflect:2.1.0")
     implementation("org.jetbrains.kotlin:kotlin-stdlib-jdk8:2.1.0")
     implementation("org.springframework.boot:spring-boot-configuration-processor:3.4.1")