patch 8.2.0638: MS-Windows: messages test fails

Problem:    MS-Windows: messages test fails.
Solution:   Clear environment variables.

src/testdir/test_messages.vim

@@ -9,6 +9,9 @@ function Test_messages()
     set nomore
     " Avoid the "message maintainer" line.
     let $LANG = ''
+    let $LC_ALL = ''
+    let $LC_MESSAGES = ''
+    let $LC_COLLATE = ''
 
     let arr = map(range(10), '"hello" . v:val')
     for s in arr

src/version.c

@@ -746,6 +746,8 @@ static char *(features[]) =
 
 static int included_patches[] =
 {   /* Add new patch number below this line */
+/**/
+    638,
 /**/
     637,
 /**/