patch 9.1.0091: Syntax test fails when run with non C locale

Problem:  Syntax test fails when run with non C locale
Solution: Run syntax tests with C locale, clean up Xtestscript file,
          strip environment variables from GetVimCommand()
          (h-east)

closes: #14007

Co-authored-by: h-east <h.east.727@gmail.com>
Signed-off-by: h-east <h.east.727@gmail.com>
Signed-off-by: Christian Brabandt <cb@256bit.org>
diff --git a/src/testdir/shared.vim b/src/testdir/shared.vim
index 4d008a0..9479efb 100644
--- a/src/testdir/shared.vim
+++ b/src/testdir/shared.vim
@@ -300,7 +300,8 @@
   endif
   let cmd .= ' --not-a-term'
   let cmd .= ' --gui-dialog-file guidialogfile'
-  let cmd = substitute(cmd, 'VIMRUNTIME=\S\+', '', '')
+  " remove any environment variables
+  let cmd = substitute(cmd, '[A-Z_]*=\S\+ *', '', 'g')
 
   " If using valgrind, make sure every run uses a different log file.
   if cmd =~ 'valgrind.*--log-file='
diff --git a/src/version.c b/src/version.c
index 6beeabb..91abfe1 100644
--- a/src/version.c
+++ b/src/version.c
@@ -705,6 +705,8 @@
 static int included_patches[] =
 {   /* Add new patch number below this line */
 /**/
+    91,
+/**/
     90,
 /**/
     89,