Fix failing CI

[imjoehaines]

Goal

CI has been failing recently because the Maze Runner fixtures no longer build successfully:

Unable to find a compatible set of packages based on your non-dev requirements alone.
Your requirements can be resolved successfully when require-dev packages are present.
You may need to move packages from require-dev or some of their dependencies to require.

Problem 1
- Root composer.json requires bugsnag/bugsnag-symfony dev-master as 99.99.99, found bugsnag/bugsnag-symfony[dev-main] but it does not match the constraint. Perhaps dev-master was renamed to dev-main?

This error seems to be caused by Composer no longer accepting dev-master in a package installed from a directory, which is how we install bugsnag-symfony in the test fixtures

This seems to be caused by composer/composer#10372, though that PR adds an alias for dev-master so I'm not 100% sure I haven't been able to reproduce this outside of this repo, so I'm assuming it's something weird we're doing

Finally, there was an unrelated error caused by cucumber/gherkin failing to parse something from its own test suite:

features/fixtures/symfony-4/bugsnag-symfony/vendor/bundle/ruby/3.0.0/gems/gherkin-5.1.0/spec/gherkin/stream/test_fr.feature: Parser errors:
15
expected: #EOF, #Language, #TagLine, #FeatureLine, #Comment, #Empty, got 'Fonctionnalité: Bonjour'
16
expected: #EOF, #Language, #TagLine, #FeatureLine, #Comment, #Empty, got 'Scénario: Monde'
17
expected: #EOF, #Language, #TagLine, #FeatureLine, #Comment, #Empty, got 'Soit une étape' (Cucumber::Core::Gherkin::ParseError)
18
https://github.com/bugsnag/bugsnag-symfony/runs/4804287510?check_suite_focus=true#step:5:14

I'm not sure this started happening when we have a lock file for Maze Runner & its dependencies, but I've also fixed this

[twometresteve]

LGTM pending successful CI.