Add the Minecraft version as a cache input to the download assets task.

This fixes an issue where the assets index would not be generated when the minecraft version changes without the assets changing.

src/main/java/net/fabricmc/loom/task/DownloadAssetsTask.java

@@ -61,6 +61,9 @@ public abstract class DownloadAssetsTask extends AbstractLoomTask {
 	@Input
 	public abstract Property<String> getAssetsHash();
 
+	@Input
+	public abstract Property<String> getMinecraftVersion();
+
 	@OutputDirectory
 	public abstract RegularFileProperty getAssetsDirectory();
 
@@ -74,6 +77,8 @@ public DownloadAssetsTask() {
 
 		getAssetsDirectory().set(assetsDir);
 		getAssetsHash().set(versionInfo.assetIndex().sha1());
+		getMinecraftVersion().set(versionInfo.id());
+		getMinecraftVersion().finalizeValue();
 
 		if (versionInfo.assets().equals("legacy")) {
 			getLegacyResourcesDirectory().set(new File(assetsDir, "/legacy/" + versionInfo.id()));