Mark junit test cases as skipped if no pickle step results available

[mrsheepuk]

🤔 What's changed?

This allows the junit reporter not to panic if the StopOnFirstFailure flag is used. It marks any subsequent test cases as 'skipped' (seemed like the best choice).

I kept the change as small as possible by recovering from the panics, instead of introducing a suite of "non-must' equivalents on the Storage struct. While that would have been far cleaner as code (recovering from panics feels decidedly icky), this solves the issue with relatively little impact to anything else. But if y'all think adding non-must equivalents onto the Storage struct is a better call, happy to make that change.

⚡️ What's your motivation?

Fixes #387

🏷️ What kind of change is this?

• 🐛 Bug fix (non-breaking change which fixes a defect)

📋 Checklist:

• I agree to respect and uphold the Cucumber Community Code of Conduct
• Users should know about my change
  • I have added an entry to the "Unreleased" section of the CHANGELOG, linking to this pull request.

[codecov]

Codecov Report

Attention: Patch coverage is 75.00000% with 9 lines in your changes are missing coverage. Please review.

Project coverage is 83.27%. Comparing base (153db4e) to head (e82afb8).
Report is 6 commits behind head on main.

Files	Patch %	Lines
internal/formatters/fmt_junit.go	75.00%	4 Missing and 5 partials ⚠️

Additional details and impacted files

@@            Coverage Diff             @@
##             main     #597      +/-   ##
==========================================
+ Coverage   83.21%   83.27%   +0.06%     
==========================================
  Files          28       29       +1     
  Lines        3413     2858     -555     
==========================================
- Hits         2840     2380     -460     
+ Misses        458      357     -101     
- Partials      115      121       +6     

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