feat: pair Testbench with Laravel version

[rivanuff]

Derives orchestra/testbench from the Laravel matrix value (L10->8, L11->9, L12->10) so consumers can test multiple Laravel majors without invalid cross-product combos. Backward compatible: existing single-value callers resolve to the same pair. The testbench-versions input remains declared but unused.

Update: both run-laravel-testbench-tests.yml and run-pest-tests.yml now derive the PHP matrix from composer.json via typisttech/php-matrix-action, and cover the dependency range via composer update (highest) vs composer update --prefer-lowest (lowest) instead of pinning explicit Laravel/testbench combinations. The php-versions, laravel-versions, and testbench-versions inputs are now deprecated/ignored (kept for backward compatibility). The two workflows have converged on the same job structure.

[Copilot]

Pull request overview

Updates the reusable GitHub Actions workflow to derive the orchestra/testbench version from the selected Laravel version in the matrix, preventing invalid Laravel/Testbench cross-product combinations when testing multiple Laravel majors.

Changes:

• Removes testbench from the strategy matrix (no longer sourced from inputs.testbench-versions).
• Adds a shell case mapping from matrix.laravel to an appropriate Testbench constraint and uses it during composer require.

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[ictbeheer]

@SimonvanWijhe en @rivanuff ik zou dit juist minder complex willen maken. Is dit alleen nodig om Acorn 4 compatibiliteit te behouden? Kunnen we het anders niet afkijken van spatie: https://github.com/spatie/laravel-data/actions/runs/33497179425/workflow