patch 8.2.0423: in some environments a few tests are expected to fail

Problem:    In some environments a few tests are expected to fail.
Solution:   Add $TEST_MAY_FAIL to list tests that should not cause make to
            fail.
diff --git a/src/version.c b/src/version.c
index a6112ce..198c42a 100644
--- a/src/version.c
+++ b/src/version.c
@@ -739,6 +739,8 @@
 static int included_patches[] =
 {   /* Add new patch number below this line */
 /**/
+    423,
+/**/
     422,
 /**/
     421,