ci: spelling: update to 0.0.15a; update whitelist

[jsoref]

Summary of the Pull Request

• Cleaning up the whitelist a bit.

  • The magic to exclude repeated characters worked 👍

  • Every successful run on master now logs its suggested cleanup, e.g. for 5740e19 has https://github.com/microsoft/terminal/runs/596271627#step:4:37

• ⚠️ This check-spelling 0.0.15a+ tolerates Windows line endings in the whitelist.txt file (another project I touched had some .gitconfig magic which required supporting them).

  This means that if someone edits the file w/ something that likes Windows line endings, the file will successfully convert (instead of it being ignored and check-spelling complaining about everything). Most likely anyone else who then edits the file will use something that will maintain the line endings.

References

PR Checklist

• Closes #xxx
• CLA signed. If not, go over here and sign the CLA
• Tests added/passed
• Requires documentation to be updated
• I've discussed this with core contributors already. If not checked, I'm ready to accept this work might be rejected in favor of a different grand plan. Issue number where discussion took place: #xxx

Detailed Description of the Pull Request / Additional comments

Validation Steps Performed

[zadjii-msft]

Thanks for staying on top of this!

[DHowett-MSFT]

Thanks!