[crypto-awslc] update aws-lc-rs to 1.7.3

[tomleavy]

Description of changes:

Update to aws-lc-rs 1.7.3 and pin to it so we don't get drifting aws-lc-sys versions again

By submitting this pull request, I confirm that my contribution is made under the terms of the Apache 2.0 and MIT license.

[codecov-commenter]

Codecov Report

All modified and coverable lines are covered by tests ✅

Project coverage is 89.61%. Comparing base (f4af668) to head (b2637f8).

Additional details and impacted files

@@            Coverage Diff             @@
##             main     #159      +/-   ##
==========================================
- Coverage   89.63%   89.61%   -0.02%     
==========================================
  Files         174      174              
  Lines       31507    31497      -10     
==========================================
- Hits        28240    28225      -15     
- Misses       3267     3272       +5     

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