build(deps): bump io.projectreactor:reactor-core from 3.6.2 to 3.6.4

Bumps [io.projectreactor:reactor-core](https://github.com/reactor/reactor-core) from 3.6.2 to 3.6.4.
- [Release notes](https://github.com/reactor/reactor-core/releases)
- [Commits](reactor/reactor-core@v3.6.2...v3.6.4)

---
updated-dependencies:
- dependency-name: io.projectreactor:reactor-core
  dependency-type: direct:production
  update-type: version-update:semver-patch
...

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

providers/jikkou-provider-kafka/pom.xml

@@ -23,7 +23,7 @@
 
     <properties>
         <license.header.file>${project.parent.basedir}/header</license.header.file>
-        <reactor-core.version>3.6.2</reactor-core.version>
+        <reactor-core.version>3.6.4</reactor-core.version>
     </properties>
 
     <dependencies>

server/jikkou-api-server/pom.xml

@@ -120,7 +120,7 @@
         <dependency>
             <groupId>io.projectreactor</groupId>
             <artifactId>reactor-core</artifactId>
-            <version>3.6.2</version>
+            <version>3.6.4</version>
         </dependency>
         <dependency>
             <groupId>io.micronaut</groupId>