patch 8.2.0156: various typos in source files and tests

Problem:    Various typos in source files and tests.
Solution:   Fix the typos. (Emir Sari, closes #5532)
diff --git a/src/gui_photon.c b/src/gui_photon.c
index 963cabc..1a7288b 100644
--- a/src/gui_photon.c
+++ b/src/gui_photon.c
@@ -1206,7 +1206,7 @@
 
     /*
      * Now that the text area widget has been created, set up the colours,
-     * which wil call PtSetResource from gui_mch_new_colors
+     * which will call PtSetResource from gui_mch_new_colors
      */
 
     /*