The CI jobs for dev dependencies do not actually test dev dependencies

[stof]

The CI workflows configures the minimum-stability for this job:

panther/.github/workflows/ci.yml

Line 90 in bc606ef

run: composer config minimum-stability dev

However, the committed composer.json already allows this stability while using prefer-stable: true:

panther/composer.json

Lines 45 to 46 in bc606ef

	"minimum-stability": "dev",
	"prefer-stable": true,

a consequence of that setup is that #682 did not actually ran the CI against Symfony 8.0.x-dev but against 7.3.6 in those jobs (and so missed the fact that the code is not actually compatible with Symfony 8, as reported in #685)