ci: add test for multiple os

[greenhandatsjtu]

Test project on multiple operating systems via matrix.
ref: casbin/casbin-rs#234
credit to: https://github.com/diesel-rs/diesel/blob/0c6219f5bd9641eea09c6fa7dca4995aefda30a0/.github/workflows/ci.yml

[casbin-bot]

@smrpn @hackerchai @PsiACE @GopherJ please review

[codecov-commenter]

Codecov Report

Merging #65 (fe0f57c) into master (018d362) will not change coverage.
The diff coverage is n/a.

@@           Coverage Diff           @@
##           master      #65   +/-   ##
=======================================
  Coverage   76.64%   76.64%           
=======================================
  Files           4        4           
  Lines         364      364           
=======================================
  Hits          279      279           
  Misses         85       85           

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[hsluoyz]

@hackerchai @PsiACE

[hackerchai]

@greenhandatsjtu Can you also make a PR to https://github.com/casbin-rs/sqlx-adapter/ ?

[PsiACE]

LGTM

[greenhandatsjtu]

@greenhandatsjtu Can you also make a PR to casbin-rs/sqlx-adapter ?

Sure, I've been working on it for a while, will make a PR this week.