patch 8.2.3914: various spelling mistakes in comments

Problem:    Various spelling mistakes in comments.
Solution:   Fix the mistakes. (Dominique Pellé, closes #9416)
diff --git a/src/vim9execute.c b/src/vim9execute.c
index 9814f25..fd53630 100644
--- a/src/vim9execute.c
+++ b/src/vim9execute.c
@@ -544,7 +544,7 @@
 	    int refcount = pt->pt_refcount;
 	    int i;
 
-	    // A Reference in a local variables doesn't count, it gets
+	    // A Reference in a local variable doesn't count, it gets
 	    // unreferenced on return.
 	    for (i = 0; i < dfunc->df_varcount; ++i)
 	    {