chore: bump paper to 1.20.4; fix warnings

We should probably keep kaboom plugins' API version synced with the main
server

pom.xml

@@ -15,7 +15,7 @@
         <dependency>
             <groupId>io.papermc.paper</groupId>
             <artifactId>paper-api</artifactId>
-            <version>1.19.4-R0.1-SNAPSHOT</version>
+            <version>1.20.4-R0.1-SNAPSHOT</version>
             <scope>provided</scope>
         </dependency>
     </dependencies>

src/main/java/pw/kaboom/commandspy/Main.java

@@ -25,6 +25,7 @@ public final class Main extends JavaPlugin implements CommandExecutor, Listener
     public void onEnable() {
         this.config = new CommandSpyState(new File(this.getDataFolder(), "state.bin"));
 
+        //noinspection DataFlowIssue
         this.getCommand("commandspy").setExecutor(this);
         this.getServer().getPluginManager().registerEvents(this, this);
 

src/main/resources/plugin.yml

@@ -1,7 +1,7 @@
 name: CommandSpy
 main: pw.kaboom.commandspy.Main
 description: Plugin that allows you to spy on players' commands.
-api-version: '1.19'
+api-version: '1.20'
 version: master
 folia-supported: true