Bump org.springframework.boot from 2.6.3 to 2.6.4

Bumps [org.springframework.boot](https://github.com/spring-projects/spring-boot) from 2.6.3 to 2.6.4.
- [Release notes](https://github.com/spring-projects/spring-boot/releases)
- [Commits](spring-projects/spring-boot@v2.6.3...v2.6.4)

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

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

build.gradle

@@ -1,7 +1,7 @@
 plugins {
     id("jacoco")
     id("com.diffplug.spotless") version "6.3.0" apply true
-    id("org.springframework.boot") version "2.6.3" apply false
+    id("org.springframework.boot") version "2.6.4" apply false
     id("io.spring.dependency-management") version "1.0.11.RELEASE" apply false
     id("org.jetbrains.kotlin.jvm") version "1.6.10" apply false
     id("org.jetbrains.kotlin.plugin.allopen") version "1.6.10" apply false