PHPunit failures fromtest_timezone_lang_strings not helpful, and America/Nuuk string missing

To reproduce:

1. Try to work on Moodle code.
2. Let Travis run PHPunit to see if your code is ready for integration.

Expect result: PHPunit passes because my code is awesome

Acutal result: core_date_testcase::test_timezone_lang_strings Failed asserting that false is true.

That message does not help you understand what the problem is. It needs to be improved.

Edited (Eloy): For the records the problems reported with 'America/Nuuk' come with the update to IANA timezone database 2020.a (that was packaged into PHP's timezonedb 2020.1 some days ago). Sites using that timezonedb (like travis, that recently updated to PHP 7.4.6) are the ones failing.

Edited 2 (Eloy): Other sources of information that can be useful (not needed in this issue but in others, timezone related):

• IANA DB source: https://www.iana.org/time-zones (CHANGELOG: https://data.iana.org/time-zones/tzdb/NEWS)
• MS TZ names: https://en.wikipedia.org/wiki/List_of_tz_database_time_zones
• Unicode Windows / IANA mapping: https://github.com/unicode-org/cldr/blob/master/common/supplemental/windowsZones.xml