tools/testing: keep legacy generated files around in .gitignore file

People keep removing generated files from .gitignore files even when the
files stay around.  Please don't do that: just because the file is no
longer being generated doesn't make it magically go away, and doesn't
make it suddenly be something that should now not be ignored any more.

Fixes: dd2c6ec ("selftests/mm: remove virtual_address_range test")
Cc: Lorenzo Stoakes <lorenzo.stoakes@oracle.com>
Cc: SeongJae Park <sj@kernel.org>
Cc: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>

Author: torvalds

tools/testing/selftests/mm/.gitignore

@@ -32,6 +32,7 @@ uffd-unit-tests
 uffd-wp-mremap
 mlock-intersect-test
 mlock-random-test
+virtual_address_range
 gup_test
 va_128TBswitch
 map_fixed_noreplace