x/tools/gopls: TestMarkers/implementation/generics.txt failure

[findleyr]

There is one failure from #60584 that seems to be of a different nature:

https://build.golang.org/log/6b41887dc7ce6783c1f3b91a04932ddb4ba6ada8

--- FAIL: TestMarkers (124.23s)
    --- FAIL: TestMarkers/implementation/generics.txt (1.10s)
        marker.go:488: other/other.go:7:54 (implementation/generics.txt:30:54): implementation: incorrect result locations: (got 0, want 1):
              []string{
            - 	"implementation/implementation.go:11:6-19 (implementation/generics.txt:21:6-19)",
              }
    marker.go:463: (Filenames are relative to /tmp/buildlet/gopath/src/golang.org/x/tools/gopls/internal/regtest/marker/testdata.)

I suspect that this could be a race to instance expansion causing it to miss methods (which would also explain some rare type error reported by users).

[findleyr]

I feel pretty confident this is #61561.

[gopherbot]

Change https://go.dev/cl/512636 mentions this issue: gopls/internal/lsp/cache: memoize active packages after every operation