fix: Treat BusinessTeam as a regular Team for Environment reviewers

[JamBalaya56562]

Fixes: #4457.
Closes: #4456.

Supersedes #4456 by @JWilkinsonMB, which has been waiting on the Google CLA since August. This is the same change, rebased onto current master (Ptr(...) is replaced with new(...), following the rest of the package). All credit for the fix goes to @JWilkinsonMB.

When an Enterprise Team is a required reviewer of an environment, the API returns "type": "BusinessTeam", so RequiredReviewer.UnmarshalJSON fails and any environment that has such a reviewer cannot be read. This treats BusinessTeam as a Team: the reviewer is decoded into a *Team and Type is set to "Team", so existing callers (such as the Terraform provider) keep working without changes.

Note that the OpenAPI descriptions still list only User and Team for deployment-reviewer-type; the BusinessTeam value comes from the API responses reported in #4457 and #4456.

Verified locally: go build ./..., go vet -tags integration ./test/integration/, go test ./... (100% coverage of RequiredReviewer.UnmarshalJSON), and custom-gcl 0 issues.

[gemini-code-assist]

Code Review

This pull request adds support for unmarshaling the 'BusinessTeam' reviewer type (used for Enterprise Teams) and treating it as a 'Team' type for compatibility, along with corresponding unit tests. Feedback was provided to improve the error message when unmarshaling fails: using %T on reviewer.Type (a *string) prints the Go type '*string' rather than the actual invalid string value, so it is recommended to dereference the pointer and format it with '%q' instead.

[codecov]

Codecov Report

✅ All modified and coverable lines are covered by tests.
✅ Project coverage is 98.61%. Comparing base (af24e38) to head (09d05a2).

Additional details and impacted files

@@           Coverage Diff           @@
##           master    #4638   +/-   ##
=======================================
  Coverage   98.61%   98.61%           
=======================================
  Files         199      199           
  Lines       18689    18694    +5     
=======================================
+ Hits        18431    18436    +5     
  Misses        258      258           

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[JWilkinsonMB]

@JamBalaya56562 - Thanks for taking this up! Still hope to get the CLA agreed for next time but it's not been a quick process...

[gmlewis]

Thank you, @JamBalaya56562 and @JWilkinsonMB!
LGTM.
Awaiting second LGTM+Approval from any other contributor to this repo before merging.

cc: @stevehipwell - @Not-Dhananjay-Mishra

[Not-Dhananjay-Mishra]

LGTM

[gmlewis]

Thank you, @Not-Dhananjay-Mishra!
Merging.