ci: set GOTOOLCHAIN=local for unit tests

[nsrip-dd]

What does this PR do?

Set GOTOOLCHAIN=local for our unit tests.

I didn't change the go get -u smoke tests. Those tests are inherently incompatible with GOTOOLCHAIN=local. We could perhaps make them work with GOTOOLCHAIN=local by adding [email protected] to the go get -u commands, like Orhcestrion does.

Motivation

Users may build our library with GOTOOLCHAIN=local. If they do, and our go.mod file specifies a newer Go version than their local toolchain, their build will break. Run our tests with GOTOOLCHAIN=local to ensure that our library builds with all of the Go versions we claim to support, without having to download a newer one.

[pr-commenter[bot]]

Benchmarks

Benchmark execution time: 2024-08-29 16:04:25

Comparing candidate commit e39271d596f35eb4796ae05d49e9cdd185f9c920 in PR branch nick.ripley/gotoolchain with baseline commit e7ca17ef602cfdaa5b0c19b219a13306bdbb757a in branch main.

Found 0 performance improvements and 0 performance regressions! Performance is the same for 59 metrics, 0 unstable metrics.