Update dependency org.springframework.boot:spring-boot-maven-plugin to v2.6.6

Author: renovate-bot

pom.xml

@@ -26,7 +26,7 @@
         <project.build.sourceEncoding>UTF-8</project.build.sourceEncoding>
         <project.reporting.outputEncoding>UTF-8</project.reporting.outputEncoding>
         <java.version>1.8</java.version>
-        <spring-boot.version>2.3.0.RELEASE</spring-boot.version>
+        <spring-boot.version>2.6.6</spring-boot.version>
         <kotlin.version>1.3.72</kotlin.version>
         <maven-compiler-plugin.version>3.8.1</maven-compiler-plugin.version>
         <slf4j.version>1.7.32</slf4j.version>