chore: Shard a11y tests during release workflow

[connorlanigan]

Description

This extends our existing test sharding to also apply during the release workflow.

See cloudscape-design/.github#57 for the existing sharding.

Related links, issue #, if available: n/a

How has this been tested?

n/a

Review checklist

The following items are to be evaluated by the author(s) and the reviewer(s).

Correctness

• Changes include appropriate documentation updates.
• Changes are backward-compatible if not indicated, see CONTRIBUTING.md.
• Changes do not include unsupported browser features, see CONTRIBUTING.md.
• Changes were manually tested for accessibility, see accessibility guidelines.

Security

• If the code handles URLs: all URLs are validated through the checkSafeUrl function.

Testing

• Changes are covered with new/existing unit tests?
• Changes are covered with new/existing integration tests?

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[codecov]

Codecov Report

Patch coverage has no change and project coverage change: -0.03% ⚠️

Comparison is base (af48159) 94.01% compared to head (6d8af26) 93.99%.

Additional details and impacted files

@@            Coverage Diff             @@
##             main    #1547      +/-   ##
==========================================
- Coverage   94.01%   93.99%   -0.03%     
==========================================
  Files         644      644              
  Lines       17364    17364              
  Branches     5710     5710              
==========================================
- Hits        16325    16321       -4     
- Misses        970      974       +4     
  Partials       69       69              

see 2 files with indirect coverage changes

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