fix: backend/pom.xml to reduce vulnerabilities

The following vulnerabilities are fixed with an upgrade:
- https://snyk.io/vuln/SNYK-JAVA-ORGSPRINGFRAMEWORKSECURITY-5777882
- https://snyk.io/vuln/SNYK-JAVA-ORGSPRINGFRAMEWORKSECURITY-5777893

Author: snyk-bot

backend/pom.xml

@@ -16,7 +16,7 @@
 
 	<properties>
 		<java.version>17</java.version>
-		<spring.version>3.0.5</spring.version>
+		<spring.version>3.0.9</spring.version>
 		<kotlin.version>1.8.21</kotlin.version>
 		<testcontainers.version>1.17.6</testcontainers.version>
 		<commit.hash>COMMIT_TO_CHANGE</commit.hash>