Bump spring.version from 2.6.6 to 3.1.0 in /backend

Bumps `spring.version` from 2.6.6 to 3.1.0.

Updates `spring-boot-starter-web` from 2.6.6 to 3.1.0
- [Release notes](https://github.com/spring-projects/spring-boot/releases)
- [Commits](spring-projects/spring-boot@v2.6.6...v3.1.0)

Updates `spring-boot-starter-actuator` from 2.6.6 to 3.1.0
- [Release notes](https://github.com/spring-projects/spring-boot/releases)
- [Commits](spring-projects/spring-boot@v2.6.6...v3.1.0)

Updates `spring-boot-starter-json` from 2.6.6 to 3.1.0
- [Release notes](https://github.com/spring-projects/spring-boot/releases)
- [Commits](spring-projects/spring-boot@v2.6.6...v3.1.0)

Updates `spring-boot-starter-security` from 2.6.6 to 3.1.0
- [Release notes](https://github.com/spring-projects/spring-boot/releases)
- [Commits](spring-projects/spring-boot@v2.6.6...v3.1.0)

Updates `spring-boot-starter-data-jpa` from 2.6.6 to 3.1.0
- [Release notes](https://github.com/spring-projects/spring-boot/releases)
- [Commits](spring-projects/spring-boot@v2.6.6...v3.1.0)

Updates `spring-boot-devtools` from 2.6.6 to 3.1.0
- [Release notes](https://github.com/spring-projects/spring-boot/releases)
- [Commits](spring-projects/spring-boot@v2.6.6...v3.1.0)

Updates `spring-boot-configuration-processor` from 2.6.6 to 3.1.0
- [Release notes](https://github.com/spring-projects/spring-boot/releases)
- [Commits](spring-projects/spring-boot@v2.6.6...v3.1.0)

Updates `spring-boot-starter-cache` from 2.6.6 to 3.1.0
- [Release notes](https://github.com/spring-projects/spring-boot/releases)
- [Commits](spring-projects/spring-boot@v2.6.6...v3.1.0)

Updates `spring-boot-starter-test` from 2.6.6 to 3.1.0
- [Release notes](https://github.com/spring-projects/spring-boot/releases)
- [Commits](spring-projects/spring-boot@v2.6.6...v3.1.0)

Updates `spring-boot-starter-log4j2` from 2.6.6 to 3.1.0
- [Release notes](https://github.com/spring-projects/spring-boot/releases)
- [Commits](spring-projects/spring-boot@v2.6.6...v3.1.0)

---
updated-dependencies:
- dependency-name: org.springframework.boot:spring-boot-starter-web
  dependency-type: direct:production
  update-type: version-update:semver-major
- dependency-name: org.springframework.boot:spring-boot-starter-actuator
  dependency-type: direct:production
  update-type: version-update:semver-major
- dependency-name: org.springframework.boot:spring-boot-starter-json
  dependency-type: direct:production
  update-type: version-update:semver-major
- dependency-name: org.springframework.boot:spring-boot-starter-security
  dependency-type: direct:production
  update-type: version-update:semver-major
- dependency-name: org.springframework.boot:spring-boot-starter-data-jpa
  dependency-type: direct:production
  update-type: version-update:semver-major
- dependency-name: org.springframework.boot:spring-boot-devtools
  dependency-type: direct:production
  update-type: version-update:semver-major
- dependency-name: org.springframework.boot:spring-boot-configuration-processor
  dependency-type: direct:production
  update-type: version-update:semver-major
- dependency-name: org.springframework.boot:spring-boot-starter-cache
  dependency-type: direct:production
  update-type: version-update:semver-major
- dependency-name: org.springframework.boot:spring-boot-starter-test
  dependency-type: direct:development
  update-type: version-update:semver-major
- dependency-name: org.springframework.boot:spring-boot-starter-log4j2
  dependency-type: direct:production
  update-type: version-update:semver-major
...

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

backend/pom.xml

@@ -16,7 +16,7 @@
 
 	<properties>
 		<java.version>17</java.version>
-		<spring.version>3.0.5</spring.version>
+		<spring.version>3.1.0</spring.version>
 		<kotlin.version>1.8.21</kotlin.version>
 		<testcontainers.version>1.17.6</testcontainers.version>
 		<commit.hash>COMMIT_TO_CHANGE</commit.hash>