Bug 37490: Add a test to detect when yarn.lock is not updated

Bug 37490: Add a test to detect when yarn.lock is not updated

to test...

1/ set koha repo to state where yarn.lock is not updated

    $ git reset --hard 67db70d4

2/ run test, observe FAIL

    $ prove ./xt/verify-yarnlock.t
    ./xt/verify-yarnlock.t .. error Your lockfile needs to be updated, but yarn was run with `--frozen-lockfile`.
    ./xt/verify-yarnlock.t .. 1/1
    #   Failed test 'verify yarn.lock file is updated correctly'
    ...
    Result: FAIL

3/ set koha repo to state where yarn.lock is updated

    $ yarn install

4/ note yarn.lock is now updated

    $ git status
    ...
    modified:   yarn.lock

5/ run test, observe SUCCESS

    $ prove -v ./xt/verify-yarnlock.t
    ./xt/verify-yarnlock.t ..
    ok 1 - verify yarn.lock file is updated correctly
    All tests successful.
    Files=1, Tests=1,  1 wallclock secs ( 0.02 usr  0.01 sys +  1.16 cusr  0.27 csys =  1.46 CPU)
    Result: PASS

Signed-off-by: Matt Blenkinsop <matt.blenkinsop@ptfs-europe.com>
Signed-off-by: Martin Renvoize <martin.renvoize@ptfs-europe.com>
Signed-off-by: Katrin Fischer <katrin.fischer@bsz-bw.de>