PY-12634 Highlight decorator with space between '@' and name

Added the same highlighting for '@' as for the name.

python/testSrc/com/jetbrains/python/PythonHighlightingTest.java

@@ -370,6 +370,11 @@ public class PythonHighlightingTest extends PyTestCase {
     runWithLanguageLevel(LanguageLevel.PYTHON36, () -> doTest(true, false));
   }
 
+  // PY-12634
+  public void testSpaceBetweenAtAndDecorator() {
+    doTest(true, true);
+  }
+
   // ---
   private void doTest(final LanguageLevel languageLevel, final boolean checkWarnings, final boolean checkInfos) {
     PythonLanguageLevelPusher.setForcedLanguageLevel(myFixture.getProject(), languageLevel);