upgrade: spring boot 3.3.5 -> 3.4.3

Author: Dominick Leppich

module-core/pom.xml

@@ -5,7 +5,7 @@
     <parent>
         <groupId>org.springframework.boot</groupId>
         <artifactId>spring-boot-starter-parent</artifactId>
-        <version>3.3.5</version>
+        <version>3.4.3</version>
         <relativePath/> <!-- lookup parent from repository -->
     </parent>
     <groupId>io.goobi.vocabulary</groupId>
@@ -15,7 +15,8 @@
     <description>Spring Boot based RESTful web service for vocabulary management</description>
     <packaging>jar</packaging>
     <properties>
-        <maven.compiler.release>17</maven.compiler.release>
+        <java.version>21</java.version>
+        <maven.compiler.release>21</maven.compiler.release>
         <maven.version>3.8.8</maven.version>
 
         <project.build.sourceEncoding>UTF-8</project.build.sourceEncoding>