Bump org.flywaydb:flyway-core from 10.20.0 to 11.3.4 in /backend

Bumps [org.flywaydb:flyway-core](https://github.com/flyway/flyway) from 10.20.0 to 11.3.4.
- [Release notes](https://github.com/flyway/flyway/releases)
- [Commits](flyway/flyway@flyway-10.20.0...flyway-11.3.4)

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

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

Author: dependabot[bot]

backend/build.gradle

@@ -30,7 +30,7 @@ dependencies {
     implementation 'org.xerial:sqlite-jdbc:3.46.1.3'
     implementation 'org.hibernate.orm:hibernate-core:6.6.9.Final'
     implementation 'org.hibernate.orm:hibernate-community-dialects:6.6.9.Final'
-    implementation 'org.flywaydb:flyway-core:10.20.0'
+    implementation 'org.flywaydb:flyway-core:11.3.4'
 
     // excel
     implementation 'org.apache.poi:poi:5.4.0'