Create codeql-analysis.yml

[pelletier]

Let's try out github's CodeQL action.

[codecov]

Codecov Report

Merging #473 (5795d3b) into master (ba1b12b) will decrease coverage by 0.75%.
The diff coverage is 32.14%.

@@            Coverage Diff             @@
##           master     #473      +/-   ##
==========================================
- Coverage   93.60%   92.84%   -0.76%     
==========================================
  Files          10       12       +2     
  Lines        2266     2293      +27     
==========================================
+ Hits         2121     2129       +8     
- Misses        105      124      +19     
  Partials       40       40              

Impacted Files	Coverage Δ
tomlpub.go	0.00% <0.00%> (ø)
tomltree_write.go	94.77% <ø> (ø)
tomltree_writepub.go	0.00% <0.00%> (ø)
marshal.go	95.91% <100.00%> (+0.05%)	⬆️

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