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/gui_motif.c b/src/gui_motif.c
index d79a414..1d95651 100644
--- a/src/gui_motif.c
+++ b/src/gui_motif.c
@@ -2768,7 +2768,7 @@
     // Create the dialog message.
     // Since LessTif is apparently having problems with the creation of
     // properly localized string, we use LtoR here. The symptom is that the
-    // string sill not show properly in multiple lines as it does in native
+    // string is not shown properly in multiple lines as it does in native
     // Motif.
     label = XmStringCreateLtoR((char *)message, STRING_TAG);
     if (label == NULL)