chore(docs): add tracestate and whitespace to spelling list

[brettlangdon]

Update the spelling list to include the words tracestate and whitespace which are needed for the build_docs job to complete successfully.

https://app.circleci.com/pipelines/github/DataDog/dd-trace-py/31885/workflows/36b716a8-d8dd-420f-b078-6b7a9eaa72c0/jobs/2157818

Checklist

• Change(s) are motivated and described in the PR description.
• Testing strategy is described if automated tests are not included in the PR.
• Risk is outlined (performance impact, potential for breakage, maintainability, etc).
• Change is maintainable (easy to change, telemetry, documentation).
• Library release note guidelines are followed.
• Documentation is included (in-code, generated user docs, public corp docs).
• Author is aware of the performance implications of this PR as reported in the benchmarks PR comment.

Reviewer Checklist

• Title is accurate.
• No unnecessary changes are introduced.
• Description motivates each change.
• Avoids breaking API changes unless absolutely necessary.
• Testing strategy adequately addresses listed risk(s).
• Change is maintainable (easy to change, telemetry, documentation).
• Release note makes sense to a user of the library.
• Reviewer is aware of, and discussed the performance implications of this PR as reported in the benchmarks PR comment.

[brettlangdon]

This PR targets 1.8 branch.

[brettlangdon]

I need to override merge requirements because require-checklist job does not exist on the 1.8 branch.