PHPLIB-858: Add MongoDB 6.0 to GitHub CI matrix

[aleksandr-rudo]

https://jira.mongodb.org/browse/PHPLIB-858

[jmikola]

There was one test failure, but it appears to be unrelated. Likely just another flaky change stream test for sharded clusters:

MongoDB.Tests.Operation.WatchFunctionalTest.testNextAdvancesKey
 [2022/05/23 22:32:34.665] FAILURE:  (PHPUnit\Framework\ExpectationFailedException)
 [2022/05/23 22:32:34.665] MongoDB\Tests\Operation\WatchFunctionalTest::testNextAdvancesKey
 [2022/05/23 22:32:34.665] Failed asserting that null is identical to 1.
 [2022/05/23 22:32:34.665] /data/mci/cafef06d16c376cb3e1ba9a9592540e1/src/tests/Operation/WatchFunctionalTest.php:1079

I restarted the Evergreen task and it passed on the second run.

[jmikola]

@aleksandr-rudo: Please hold off on merging this. I just realized that the corresponding PHPC PR (mongodb/mongo-php-driver#1323) encountered a build failure attempting to download http://downloads.10gen.com/linux/mongodb-linux-x86_64-enterprise-debian92-6.0.0-rc5.tgz.

Since PHPLIB does not include 6.0 in its CI matrix for PRs, we didn't see an error here. I'll dig into this a bit to see what's wrong.

[jmikola]

While we wait for the PHP toolchain to be deployed to Debian 10+ (BUILD-15059), please amend this PR to test MongoDB 6.0 on GitHub CI.

[jmikola]

GitHub CI changes look good. Let's just remove the Evergreen changes for now and merge with only GitHub. Then we can bump PHPLIB-858 back to blocked on the corresponding BUILD ticket and deal with Evergreen in a second PR.