Allow sync langpack only sync file if changed since last sync

[Robert Lyon]

If you have lang pack syncing as part of an automated process it can mean trying to sync lang packs multiple times in a day - but the packs don't change that often.

So I'll make some changes to the sync so that it only updates lang pack if newer upstream file

[Mahara Bot (dev-mahara)]

Patch for "master" branch: https://reviews.mahara.org/10136

[Mahara Bot (dev-mahara)]

Reviewed: https://reviews.mahara.org/10136
Committed: https://git.mahara.org/mahara/mahara/commit/9da2f4ed4be33ed661fa6ecc62faaa979383e563
Submitter: Cecilia Vela Gurovic (<email address hidden>)
Branch: master

commit 9da2f4ed4be33ed661fa6ecc62faaa979383e563
Author: Robert Lyon <email address hidden>
Date: Fri Jun 28 09:28:17 2019 +1200

Bug 1834544: Allow sync to be ignored if upstream file hasn't changed

We do this by setting our local temp copy of langpack to the same
modified time as upstream one and comparing them on next sync

behatnotneeded

Change-Id: I2e513247fa64d33b4448d66109286d48accc8e35
Signed-off-by: Robert Lyon <email address hidden>