PHPLIB-1098: Test on RHEL 8.x

[alcaeus]

PHPLIB-1098

This follows up work in #1442 and removes RHEL 7.1 and 7.2 in favour of RHEL 8.

I've ran a previous patch for these changes: https://spruce.mongodb.com/version/64a65e1be3c331bdcdd56781/tasks?sorts=STATUS%3AASC%3BBASE_STATUS%3ADESC

Note that the zseries builds take a long time due to limited build system availability.

[jmikola]

Note, the comment above this matrix still states:

# Test all PHP versions with latest-stable MongoDB on Debian 11, Debian 10, RHEL 8.0, Ubuntu 20.04

Should it be updated to refer to RHEL 7.6 and Ubuntu 22.04 (or perhaps just say all operating systems)?

I'm not convinced that we need to test the alternative architectures with such a wide matrix. Consider moving rhel83-zseries and rhel81-power8 to the test-alt-archs matrix below (and updating the server/PHP versions as needed).

And perhaps you'd like to group the arm64 platforms together as well with a more limited matrix.

[alcaeus]

I updated the comment. As for the range that's tested, the matrix tests all supported PHP versions against the lowest and highest server versions we support. I believe that testing with all PHP versions should be part of the pipeline, but we can consider dropping one of the MongoDB server versions under test.

I'd also be in favour of differentiating between pull request and branch builds. While branch builds should test all platforms and server versions exhaustively, we may get away with limiting testing to PHP edge versions (so lowest and highest supported) in pull requests for these platforms. I'd have to take a look on how we could best configure this, but offering it as a suggestion to narrow down the PR pipeline.

[jmikola]

SGTM. I concur that we should focus on minimizing the PR builds since that's where most of the overhead comes from.