[ios] Update MGLTileSetTests.testTileSetFromTileURLTemplates for Xcode 11

[friedbunny]

Silences the failure seen in #13386 (comment) — I have not yet investigated the veracity/impact of the failure, but I’d like to stop failing tests in the meantime.

/cc @1ec5

[julianrex]

Just hit this error with https://circleci.com/gh/mapbox/mapbox-gl-native/319582, so great timing!

[friedbunny]

A few notes:

• I still haven’t looked very closely at the failure, but I think it may be an iOS 13 beta 7 or 8 thing, since this issue was introduced in Xcode 11b6.
• CircleCI uses the same 11.0.0 configuration string for each new Xcode beta, so they silently bumped us to a new image version with this failing change.
• The test is over-dependent on (evidently) very changeable HTML rendering — see -[MGLTileSetTests testTileSetFromTileURLTemplates] fails on High Sierra and above #13386.