Switch from WARN to DEBUG for empty maven targets (#1549)

Author: nedtwigg

plugin-maven/src/main/java/com/diffplug/spotless/maven/SpotlessApplyMojo.java

@@ -66,7 +66,7 @@ protected void process(Iterable<File> files, Formatter formatter, UpToDateChecke
 			getLog().info(String.format("Spotless.%s is keeping %s files clean - %s were changed to be clean, %s were already clean, %s were skipped because caching determined they were already clean",
 					formatter.getName(), counter.getTotal(), counter.getCleaned(), counter.getCheckedButAlreadyClean(), counter.getSkippedAsCleanCache()));
 		} else {
-			getLog().warn(String.format("Spotless.%s has no target files. Examine your `<includes>`: https://github.com/diffplug/spotless/tree/main/plugin-maven#quickstart", formatter.getName()));
+			getLog().debug(String.format("Spotless.%s has no target files. Examine your `<includes>`: https://github.com/diffplug/spotless/tree/main/plugin-maven#quickstart", formatter.getName()));
 		}
 	}
 }