patch 8.2.3637: typos in test files

Problem:    Typos in test files.
Solution:   Correct the typos. (Dominique Pellé, closes #9175)
diff --git a/src/testdir/test_termcodes.vim b/src/testdir/test_termcodes.vim
index f73770b..ba02584 100644
--- a/src/testdir/test_termcodes.vim
+++ b/src/testdir/test_termcodes.vim
@@ -314,8 +314,8 @@
     call setline(1, ['123456789', '123456789'])
     let @* = 'abc'
 
-    " Middle-click in inesrt mode doesn't move the cursor but inserts the
-    " contents of aregister
+    " Middle-click in insert mode doesn't move the cursor but inserts the
+    " contents of a register
     call cursor(1, 4)
     call feedkeys('i' ..
           \ MouseMiddleClickCode(2, 7) .. MouseMiddleReleaseCode(2, 7) ..
@@ -365,7 +365,7 @@
   close!
 endfunc
 
-" Test for using the mouse to increaes the height of the cmdline window
+" Test for using the mouse to increase the height of the cmdline window
 func Test_mouse_cmdwin_resize()
   CheckFeature cmdwin