Update Java 21 (#17)

* Update Java 21

* Update readme

.github/workflows/gradle.yml

@@ -16,7 +16,7 @@ jobs:
     - name: Set up Java
       uses: actions/setup-java@v2
       with:
-        java-version: '11'
+        java-version: '21'
         distribution: 'temurin'
     - name: Gradle cache
       uses: actions/cache@v3

README.md

@@ -1,5 +1,5 @@
 [![CI](https://github.com/rogervinas/spring-immutable-configuration-properties/actions/workflows/gradle.yml/badge.svg?branch=master)](https://github.com/rogervinas/spring-immutable-configuration-properties/actions/workflows/gradle.yml)
-![Java](https://img.shields.io/badge/Java-11-blue?labelColor=black)
+![Java](https://img.shields.io/badge/Java-21-blue?labelColor=black)
 ![SpringBoot](https://img.shields.io/badge/SpringBoot-2.7.17-blue?labelColor=black)
 
 # Spring Immutable @ConfigurationProperties PoC

build.gradle.kts

@@ -9,7 +9,7 @@ plugins {
 
 group = "com.example"
 version = "0.0.1-SNAPSHOT"
-java.sourceCompatibility = JavaVersion.VERSION_11
+java.sourceCompatibility = JavaVersion.VERSION_21
 
 repositories {
   mavenCentral()