Update main plugin to Java 17

All supported versions require Java 17, there's no reason the plugin should not.
Swap to Temurin for CI, Adopt is dead.

.github/workflows/ci.yml

@@ -12,7 +12,7 @@ jobs:
 
       - uses: actions/setup-java@v3
         with:
-          distribution: 'adopt'
+          distribution: 'temurin'
           java-version: '17'
           cache: 'maven'
 

pom.xml

@@ -27,8 +27,8 @@
 
   <properties>
     <project.build.sourceEncoding>UTF-8</project.build.sourceEncoding>
-    <maven.compiler.source>16</maven.compiler.source>
-    <maven.compiler.target>16</maven.compiler.target>
+    <maven.compiler.source>17</maven.compiler.source>
+    <maven.compiler.target>17</maven.compiler.target>
     <!-- Silence IDE warning - property is declared in individual internal modules. -->
     <spigot.version>unknown</spigot.version>
   </properties>