Report a step placed before the first scenario or background (#779)

[golikovichev]

Fixes #779.

Problem

gherkin-official 31 and later no longer raise a parse error when a step keyword (Given/When/Then/And/But) is placed before the first scenario or background. Instead the line is folded into the feature description. pytest-bdd relied on gherkin raising that error (mapped through ERROR_PATTERNS) to produce FeatureError: Step definition outside of a Scenario or a Background., so on newer gherkin the malformed feature was accepted silently and tests/parser/test_errors.py::test_step_outside_scenario_or_background_error started failing.

Fix

After a successful parse, pytest-bdd now checks whether the first non-empty line of the feature description starts with a step keyword and raises the same FeatureError if so. This keeps the behaviour consistent across all supported gherkin-official versions: older versions still report it through the existing parse-error path, newer versions through this post-parse check.

The check only looks at the first non-empty description line, so a legitimate multi-line description that mentions a keyword later is not affected (covered by tests/feature/test_steps.py::test_keywords_used_outside_steps). Like the existing ERROR_PATTERNS, it matches the English step keywords.

Testing

• test_step_outside_scenario_or_background_error passes again.
• test_keywords_used_outside_steps still passes (no false positive).
• Verified locally on gherkin-official 30.1.3 and 40.0.0.

[youtux]

I think we should rather have the Gherkin lead here and follow the same logic

[golikovichev]

Good call. Switched to the Gherkin dialect keywords for the feature's language instead of the hardcoded English ones, so the check follows Gherkin's own step detection and works for non-English features too. Added a French regression test.