Update dependency org.springframework.boot:spring-boot-gradle-plugin to v2.6.3

Author: renovate-bot

build.gradle

@@ -3,7 +3,7 @@ buildscript {
         mavenCentral()
     }
     dependencies {
-        classpath("org.springframework.boot:spring-boot-gradle-plugin:2.2.2.RELEASE")
+        classpath("org.springframework.boot:spring-boot-gradle-plugin:2.6.3")
     }
 }