Add support for "performed_via_github_app" and "requested_team" in IssueEvent

[Shyclyde]

Issue Source

#2945 mentions the reasoning for this PR.

Why

"performed_via_github_app" and "requested_team" are valuable results in the issue events response (when available) to determine more about the event. It also keeps the struct up to date with the API response.

What

• Adds these values to the IssueEvent struct.
• Adds test cases for added values.
• Restructures relevant test cases slightly to match the order of the given/want for easier reference.

Other notes

Ran all available test scripts, updated accordingly. Tests passing.

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[gmlewis]

Thank you, @Shyclyde !
LGTM.

Awaiting second LGTM+Approval from any other contributor to this repo before merging.

[codecov]

Codecov Report

Merging #2946 (954e7ed) into master (8cd452b) will not change coverage.
The diff coverage is n/a.

@@ Coverage Diff @@## master #2946 +/- ##
=======================================
Coverage 98.19% 98.19% =======================================
Files 145 145 Lines 12720 12720 =======================================
Hits 12490 12490 Misses 156 156 Partials 74 74 

Files	Coverage Δ
github/event_types.go	100.00% <ø> (ø)
github/issues_events.go	100.00% <ø> (ø)
github/issues_timeline.go	100.00% <ø> (ø)

[gmlewis]

Thank you, @WillAbides !
Merging.