update versions in ci.yml

[hyrodium]

• Update version of actions/checkout
  • I'm not familiar with the difference between v1 and v2, but it's better to update this.
• Fix version of julia-actions/setup-julia
  • @latest is not recommended. (See https://github.com/julia-actions/setup-julia)

[codecov]

Codecov Report

Merging #184 (9215725) into master (70680c7) will not change coverage.
The diff coverage is n/a.

@@           Coverage Diff           @@
##           master     #184   +/-   ##
=======================================
  Coverage   86.41%   86.41%           
=======================================
  Files          14       14           
  Lines        1325     1325           
=======================================
  Hits         1145     1145           
  Misses        180      180           

---

Continue to review full report at Codecov.

Legend - Click here to learn more
Δ = absolute <relative> (impact), ø = not affected, ? = missing data
Powered by Codecov. Last update 70680c7...9215725. Read the comment docs.