Bump spring-security-core from 5.1.11.RELEASE to 5.5.7 in /Server

Bumps [spring-security-core](https://github.com/spring-projects/spring-security) from 5.1.11.RELEASE to 5.5.7.
- [Release notes](https://github.com/spring-projects/spring-security/releases)
- [Changelog](https://github.com/spring-projects/spring-security/blob/main/RELEASE.adoc)
- [Commits](https://github.com/spring-projects/spring-security/compare/5.1.11.RELEASE...5.5.7)

---
updated-dependencies:
- dependency-name: org.springframework.security:spring-security-core
  dependency-type: direct:production
...

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

Server/pom.xml

@@ -114,7 +114,7 @@
         <dependency>
             <groupId>org.springframework.security</groupId>
             <artifactId>spring-security-core</artifactId>
-            <version>5.1.11.RELEASE</version>
+            <version>5.5.7</version>
         </dependency>
         <dependency>
             <groupId>com.sparkjava</groupId>