patch 9.1.0286: Vim9: E1027 with defcompile for abstract methods

Problem:  Vim9: E1027 with defcompile for abstract methods with
          non-void return types, but still compiles it
          (zzzyxwvut)
Solution: Don't compile abstract methods
          (Yegappan Lakshmanan)

fixes: #14443
closes: #14447

Signed-off-by: Yegappan Lakshmanan <yegappan@yahoo.com>
Signed-off-by: Christian Brabandt <cb@256bit.org>
diff --git a/src/vim9class.c b/src/vim9class.c
index 11e952c..a6b3ee2 100644
--- a/src/vim9class.c
+++ b/src/vim9class.c
@@ -3723,7 +3723,9 @@
 	{
 	    ufunc_T *ufunc = loop == 1 ? cl->class_class_functions[i]
 						: cl->class_obj_methods[i];
-	    defcompile_function(ufunc, cl);
+	    // Don't compile abstract methods
+	    if (!IS_ABSTRACT_METHOD(ufunc))
+		defcompile_function(ufunc, cl);
 	}
     }
 }