Bump spring-boot-gradle-plugin from 2.6.3 to 2.6.4 (#741)

Bumps [spring-boot-gradle-plugin](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:spring-boot-gradle-plugin
  dependency-type: direct:production
  update-type: version-update:semver-patch
...

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

Co-authored-by: dependabot[bot] <49699333+dependabot[bot]@users.noreply.github.com>

Author: dependabot[bot]

build.gradle

@@ -23,7 +23,7 @@ import org.springframework.boot.gradle.plugin.SpringBootPlugin
 buildscript {
     ext {
         kotlin_version = '1.6.10'
-        spring_boot_version = '2.6.3'
+        spring_boot_version = '2.6.4'
     }
 
     repositories {