patch 8.2.5165: import test fails because 'diffexpr' isn't reset

Problem:    Import test fails because 'diffexpr' isn't reset.
Solution:   Reset 'diffexpr'.
diff --git a/src/testdir/test_vim9_import.vim b/src/testdir/test_vim9_import.vim
index 415a7a9..f28b4ad 100644
--- a/src/testdir/test_vim9_import.vim
+++ b/src/testdir/test_vim9_import.vim
@@ -1234,6 +1234,8 @@
   redraw
 
   diffoff!
+  set diffexpr=
+  set diffopt&
   bwipe!
   bwipe!
   delete('Xdiffexpr')
diff --git a/src/version.c b/src/version.c
index d7f0a83..8e396cd 100644
--- a/src/version.c
+++ b/src/version.c
@@ -736,6 +736,8 @@
 static int included_patches[] =
 {   /* Add new patch number below this line */
 /**/
+    5165,
+/**/
     5164,
 /**/
     5163,