Fix typos mostly in comments, docs and test names (GH-15209)

diff --git a/Lib/tkinter/filedialog.py b/Lib/tkinter/filedialog.py
index dbb97dd..3ed93eb 100644
--- a/Lib/tkinter/filedialog.py
+++ b/Lib/tkinter/filedialog.py
@@ -469,7 +469,7 @@
     except (ImportError, AttributeError):
         pass
 
-    # dialog for openening files
+    # dialog for opening files
 
     openfilename=askopenfilename(filetypes=[("all files", "*")])
     try: