Switch testing from CircleCI to GitHub Actions

[tsalo]

Closes None.

Changes proposed in this pull request:

• Replace the CircleCI configuration with a new GitHub workflow.

To do:

• Merge coverage reports before uploading to CodeCov.
• Move the linter into a separate workflow?

[codecov]

Codecov Report

Merging #642 (c4d78ea) into main (2060739) will increase coverage by 0.22%.
The diff coverage is 100.00%.

❗ Current head c4d78ea differs from pull request most recent head 171949b. Consider uploading reports for the commit 171949b to get more accurate results

@@            Coverage Diff             @@
##             main     #642      +/-   ##
==========================================
+ Coverage   84.78%   85.00%   +0.22%     
==========================================
  Files          40       40              
  Lines        4343     4381      +38     
==========================================
+ Hits         3682     3724      +42     
+ Misses        661      657       -4     

Impacted Files	Coverage Δ
nimare/meta/cbma/ale.py	95.02% <100.00%> (+2.27%)	⬆️
nimare/meta/cbma/mkda.py	96.41% <0.00%> (+0.01%)	⬆️
nimare/meta/cbma/base.py	94.71% <0.00%> (+0.02%)	⬆️
nimare/utils.py	95.46% <0.00%> (+0.05%)	⬆️
nimare/transforms.py	75.45% <0.00%> (+0.08%)	⬆️
nimare/base.py	88.39% <0.00%> (+0.21%)	⬆️
nimare/correct.py	92.47% <0.00%> (+0.42%)	⬆️
nimare/dataset.py	89.72% <0.00%> (+0.60%)	⬆️

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[tsalo]

I need to figure out how to merge the coverage reports from each of the individual jobs.