Improve stringify test coverage

[gmlewis]

This PR adds missing structs and slices to the stringify tests for better test coverage.

[codecov]

Codecov Report

Merging #2320 (c235e4a) into master (6cd5d41) will increase coverage by 0.05%.
The diff coverage is n/a.

❗ Current head c235e4a differs from pull request most recent head 1bb88f3. Consider uploading reports for the commit 1bb88f3 to get more accurate results

@@            Coverage Diff             @@
##           master    #2320      +/-   ##
==========================================
+ Coverage   97.87%   97.92%   +0.05%     
==========================================
  Files         117      115       -2     
  Lines       10402    10416      +14     
==========================================
+ Hits        10181    10200      +19     
+ Misses        154      148       -6     
- Partials       67       68       +1     

Impacted Files	Coverage Δ
github/repos_contents.go	88.95% <0.00%> (-0.38%)	⬇️
github/github.go	97.64% <0.00%> (-0.10%)	⬇️
github/actions_artifacts.go	100.00% <0.00%> (ø)
github/actions_workflow_jobs.go	100.00% <0.00%> (ø)
github/actions_workflow_runs.go	100.00% <0.00%> (ø)
github/repos_actions_permissions.go
github/repos_actions_allowed.go
github/repos.go	98.70% <0.00%> (+0.04%)	⬆️
github/repos_stats.go	95.34% <0.00%> (+2.32%)	⬆️
github/misc.go	100.00% <0.00%> (+3.63%)	⬆️
... and 1 more

---

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 6cd5d41...1bb88f3. Read the comment docs.

[gmlewis]

@Parker77 - do you have time for a code review?

[Parker77]

LGTM!

[gmlewis]

Thank you, @Parker77 !
Merging.