Updated readme legacy windows runner references to dyn

[cbchadb35]

Summary of PR changes

PR Requirements

• For major, minor, or breaking changes, at least one of the commit messages contains the appropriate +semver: keywords.
  • See the Incrementing the Version section of the repository's README.md for more details.
• The action code does not contain sensitive information.

NOTE: If the repo's workflow could not automatically update the README.md, it should be updated manually with the next version. For javascript actions, if the repo's workflow could not automatically recompile the action it should also be updated manually as part of the PR.