fix: type for websocket header

[manchuck]

Fixes #833

Description

Motivation and Context

Testing Details

Example Output or Screenshots (if appropriate)

Types of changes

• Bug fix (non-breaking change which fixes an issue)
• New feature (non-breaking change which adds functionality)
• Breaking change (fix or feature that would cause existing functionality to change)

Checklist

• My code follows the code style of this project.
• My change requires a change to the documentation.
• I have updated the documentation accordingly.
• I have read the CONTRIBUTING document.
• I have added tests to cover my changes.
• All new and existing tests passed.

[codecov-commenter]

Codecov Report

Merging #851 (a551a80) into 3.x (f04c595) will not change coverage.
The diff coverage is n/a.

@@           Coverage Diff           @@
##              3.x     #851   +/-   ##
=======================================
  Coverage   83.42%   83.42%           
=======================================
  Files         119      119           
  Lines        1484     1484           
  Branches      283      283           
=======================================
  Hits         1238     1238           
  Misses        245      245           
  Partials        1        1           

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[dragonmantank]

LGTM