chore: Pin deps via Cargo.lock

[larseggert]

Instead of via Cargo.toml.

@mxinden is this what you head in mind for mozilla/neqo#2446? Trying it here first, since it's a smaller diff.

[codecov]

Codecov Report

All modified and coverable lines are covered by tests ✅

Project coverage is 86.72%. Comparing base (2aba0f6) to head (c78c87f).
Report is 1 commits behind head on main.

Additional details and impacted files

@@            Coverage Diff             @@
##             main      #93      +/-   ##
==========================================
- Coverage   86.90%   86.72%   -0.18%     
==========================================
  Files           5        5              
  Lines         565      565              
  Branches      565      565              
==========================================
- Hits          491      490       -1     
- Misses         48       49       +1     
  Partials       26       26              

☔ View full report in Codecov by Sentry.
📢 Have feedback on the report? Share it here.

🚀 New features to boost your workflow:

• ❄ Test Analytics: Detect flaky tests, report on failures, and find test suite problems.