fix: backend/pom.xml to reduce vulnerabilities

The following vulnerabilities are fixed with an upgrade:
- https://snyk.io/vuln/SNYK-JAVA-ORGPOSTGRESQL-3146847
- https://snyk.io/vuln/SNYK-JAVA-ORGYAML-2806360
- https://snyk.io/vuln/SNYK-JAVA-ORGYAML-3016888
- https://snyk.io/vuln/SNYK-JAVA-ORGYAML-3016889
- https://snyk.io/vuln/SNYK-JAVA-ORGYAML-3016891
- https://snyk.io/vuln/SNYK-JAVA-ORGYAML-3113851

Author: snyk-bot

Diff for: backend/pom.xml

@@ -19,7 +19,7 @@
 
 		<!-- backend dependencies -->
 		<rest-assured.version>4.5.1</rest-assured.version>
-		<postgresql.version>42.5.0</postgresql.version>
+		<postgresql.version>42.5.1</postgresql.version>
 		<groovy.version>3.0.13</groovy.version>
 	</properties>