testing: add missing Output method to testing.TB

[mateusz834]

#59928 added the Output method to T,B and F, but it was not added to TB, as initially accepted: #59928 (comment) . Thus we should add this, but as now we are in the release-freeze this will require a exception (this is a new API). This is rather a low-risk change, but it can also be deferred for 1.26.

Originally mentioned here: #59928 (comment)

CC @golang/release

[gopherbot]

Change https://go.dev/cl/677875 mentions this issue: testing: add Output method to TB

[neild]

I don't believe this needs a freeze exception: It's a bugfix in an accepted new API.

[mateusz834]

I don't believe this needs a freeze exception: It's a bugfix in an accepted new API.

I thought that any API change would need such, thanks.

[dmitshur]

Indeed—freeze exceptions would be needed for changes that aren't in scope of the freeze (and ideally they need to be filed and approved before the freeze), but finding and resolving issues in new-to-Go-1.25 features is an expected part of the freeze. Of course each bug fix still needs to be thought trough carefully, but it helps that this was caught early during the freeze, before even the first RC.