Enhancement: Add PHP 8 to build matrix

[localheinz]

This PR

• adds PHP 8 to the build matrix

💁‍♂ For reference, see shivammathur/setup-php#104.

[codecov]

Codecov Report

Merging #3979 into master will not change coverage.
The diff coverage is n/a.

@@            Coverage Diff            @@
##             master    #3979   +/-   ##
=========================================
  Coverage     85.46%   85.46%           
  Complexity     3848     3848           
=========================================
  Files           156      156           
  Lines          9719     9719           
=========================================
  Hits           8306     8306           
  Misses         1413     1413

---

Continue to review full report at Codecov.

Legend - Click here to learn more
Δ = absolute <relative> (impact), ø = not affected, ? = missing data
Powered by Codecov. Last update 0575997...80f4564. Read the comment docs.

[sebastianbergmann]

The 8.0 job uses PHP 7.3.12:

• https://github.com/sebastianbergmann/phpunit/pull/3979/checks?check_run_id=339672157#step:3:12
• https://github.com/sebastianbergmann/phpunit/pull/3979/checks?check_run_id=339672157#step:8:6

[shivammathur]

@sebastianbergmann @localheinz
Please quote these versions as GitHub Actions truncates zeros after decimal in inputs.

php-version:
  - '7.3'
  - '7.4'
  - '8.0'

[localheinz]

Thank you, @shivammathur!

[shivammathur]

@localheinz
Please note that Xdebug currently does not support this version.

[localheinz]

Thank you for clarifying, @shivammathur!

[localheinz]

Thank you, @sebastianbergmann!