Drop python 3.6 support

[JWCook]

Follow-up from #31. Python 3.6 is EOL, and poetry no longer supports it. This fixes the CI issue encountered in #76.

This also adds GitHub Actions tests for all python versions between 3.7 and 3.10.

[codecov[bot]]

Codecov Report

Base: 98.18% // Head: 98.15% // Decreases project coverage by -0.03% :warning:

Coverage data is based on head (080c765) compared to base (802d1fb). Patch has no changes to coverable lines.

Additional details and impacted files

```diff @@ Coverage Diff @@ ## master #77 +/- ## ========================================== - Coverage 98.18% 98.15% -0.04% ========================================== Files 8 7 -1 Lines 386 379 -7 Branches 33 33 ========================================== - Hits 379 372 -7 Misses 4 4 Partials 3 3 ``` | [Impacted Files](https://codecov.io/gh/vutran1710/PyrateLimiter/pull/77?src=pr&el=tree&utm_medium=referral&utm_source=github&utm_content=comment&utm_campaign=pr+comments&utm_term=Vu+Tran) | Coverage Δ | | |---|---|---| | [pyrate\_limiter/\_\_init\_\_.py](https://codecov.io/gh/vutran1710/PyrateLimiter/pull/77/diff?src=pr&el=tree&utm_medium=referral&utm_source=github&utm_content=comment&utm_campaign=pr+comments&utm_term=Vu+Tran#diff-cHlyYXRlX2xpbWl0ZXIvX19pbml0X18ucHk=) | | | Help us with your feedback. Take ten seconds to tell us [how you rate us](https://about.codecov.io/nps?utm_medium=referral&utm_source=github&utm_content=comment&utm_campaign=pr+comments&utm_term=Vu+Tran). Have a feature suggestion? [Share it here.](https://app.codecov.io/gh/feedback/?utm_medium=referral&utm_source=github&utm_content=comment&utm_campaign=pr+comments&utm_term=Vu+Tran)

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[JWCook]

Codecov Report

Base: 98.18% // Head: 98.15% // Decreases project coverage by -0.03% ⚠️

Not sure why it says coverage decreased. New coverage.py version may be counting the total number of lines differently?

[vutran1710]

Codecov Report

Base: 98.18% // Head: 98.15% // Decreases project coverage by -0.03% ⚠️

Not sure why it says coverage decreased. New coverage.py version may be counting the total number of lines differently?

Wont be a problem. Merging now.