t/README: add missing value for GIT_TEST_DEFAULT_REF_FORMAT

The documentation only lists "files" as a possible value, but
"reftable" is also valid.

Signed-off-by: Bence Ferdinandy <[email protected]>
Signed-off-by: Junio C Hamano <[email protected]>

Author: ferdinandyb

t/README

@@ -465,8 +465,9 @@ GIT_TEST_DEFAULT_HASH=<hash-algo> specifies which hash algorithm to
 use in the test scripts. Recognized values for <hash-algo> are "sha1"
 and "sha256".
 
-GIT_TEST_DEFAULT_REF_FORMAT=<format> specifies which ref storage format
-to use in the test scripts. Recognized values for <format> are "files".
+GIT_TEST_DEFAULT_REF_FORMAT=<format> specifies which ref storage format to use
+in the test scripts. Recognized values for <format> are "files" and
+"reftable".
 
 GIT_TEST_NO_WRITE_REV_INDEX=<boolean>, when true disables the
 'pack.writeReverseIndex' setting.