Update to 1.56
Add missing TEST_DEPENDS

Upstream changes:
1.56 Mon Dec 14 14:35 2020
  - Update MANIFEST to include all tests. It hasn't
    been updated in a while

1.55 Mon Dec 14 12:10 2020
  - Add ability to override internal value of 'time'
    everywhere to make tests that check expiry of items
    faster and more robust

1.54 Sat Dec 12 13:40 2020
  - Add Test::Deep as dependency to Makefile.PL

1.53 Thu Dec 10 13:40 2020
  - Handle expire_on being undef (use cache default) and
    return undef if existing value not found in cache.
    Makes get_and_set which passes on expire_on just work
    in "doesn't exist" case

1.52 Thu Dec 10 12:20 2020
  - Fix bug where a get() on a key that was expired would
    cause that key to be deleted and never written back
    even if it was dirty
  - Added new expire_on naming so that expire_time
    (relative future time) and expire_on (absolute
    unix epoch time) are now clear and distinct
  - Allow setting expire_on when doing a set() call,
    which is useful from get_and_set() to maintain
    an items absolute expiry time

1.51 Wed Nov 11 17:15 2020
  - Skip JSON/Sereal tests if modules not present
  - Updated .gitignore
    Thanks to https://github.com/szabgab/
  - GitHub Actions config file
    Thanks to https://github.com/szabgab/

1.50 Fri Nov 6 20:40 2020
  - Allow get_and_set sub to return an options
    hash passed to the internal set call

(wen)