Bump txaio from 18.8.1 to 21.2.1

[dependabot-preview[bot]]

Bumps txaio from 18.8.1 to 21.2.1.

Changelog

Sourced from txaio's changelog.

21.2.1

• fix: update minimum dependencies (here, and in other crossbar packages) in an attempt to tame the new pip dep resolver madness.

20.12.1

• new: CI/CD migrated to GitHub Actions
• new: support Python 3.9 (CI / testing added)
• new: minimum Python version is now 3.6

20.4.1

• new: upload wheel to S3 (bucket "crossbarbuilder") in CI deploy stage
• fix: fix event loop threading issue (PR #163)

20.3.1

• new: support import-time framework selection
• fix: remove python2 support (finally)

20.1.1

• IMPORTANT: beginning release v20.1.1, we only support Python 3.5 or later
• new: moved time_ns and perf_counter_ns helper functions here

Commits

• 5f8df34 bump deps to tame pip resolver (#171)
• 8e090c0 fix CI job conditional
• e00c57d fix links in readme
• 82dc835 splitup CI into two workflows
• fd7c659 also report number of AWS env vars set in CI deploy step
• 09768d7 CI fixes
• 3754400 CI fixes
• e3cfb99 fixes
• 0843f0d migrate to GH actions - part 2 (#168)
• d087ef8 add GH actions based CI (#167)
• Additional commits viewable in compare view

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