chore(deps): bump org.springframework.boot from 3.5.4 to 3.5.6

Bumps [org.springframework.boot](https://github.com/spring-projects/spring-boot) from 3.5.4 to 3.5.6.
- [Release notes](https://github.com/spring-projects/spring-boot/releases)
- [Commits](spring-projects/spring-boot@v3.5.4...v3.5.6)

---
updated-dependencies:
- dependency-name: org.springframework.boot
  dependency-version: 3.5.6
  dependency-type: direct:production
  update-type: version-update:semver-patch
...

Signed-off-by: dependabot[bot] <[email protected]>

Author: dependabot[bot]

gateway-service/build.gradle

@@ -2,7 +2,7 @@ plugins {
     id 'java'
     id "io.github.lognet.grpc-spring-boot" version '5.2.0'
     id "com.google.protobuf" version "0.9.5"
-    id 'org.springframework.boot' version '3.5.4'
+    id 'org.springframework.boot' version '3.5.6'
     id 'io.spring.dependency-management' version '1.1.7'
 }
 

greeting-service/build.gradle

@@ -1,7 +1,7 @@
 plugins {
     id 'java'
     id "io.github.lognet.grpc-spring-boot" version '5.2.0'
-    id 'org.springframework.boot' version '3.5.4'
+    id 'org.springframework.boot' version '3.5.6'
     id 'io.spring.dependency-management' version '1.1.7'
 }