ci: fix the Behat workflow setup

[mrrobot47]

The Behat jobs have been failing at setup because actions/cache@v2 is deprecated.

This PR:

• bumps actions/cache to v4;
• makes the downloaded docker-compose binary executable;
• builds the phar without dev autoloading;
• drops PHP 7.2 and 7.3 from the matrix. PHP 7.2 couldn't run the test dependencies, and neither version is supported any more (core requires PHP >= 7.4 and its CI doesn't test them).

Because of the matrix change, the required status checks need Behat Tests - PHP 7.2 and Behat Tests - PHP 7.3 removed; branch protection now requires WIP, Behat Tests - PHP 7.4 and Behat Tests - PHP 8.0.

Earlier run on the fork, before the matrix change (7.3, 7.4 and 8.0 pass; 7.2 fails on the dependency parse error): https://github.com/mrrobot47/site-type-php/actions/runs/36710563782

[Copilot]

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[Copilot]

Copilot review overview

🟢 Approval recommended

The focused workflow changes are consistent with the stated purpose and supported by successful PHP 7.4 and 8.0 runs.

Review effort: Balanced
Findings: None