cmd/go: TestScript/mod_invalid_version failures on linux-386-longtest due to missing ancestor tags

[bcmills]

--- FAIL: TestScript (0.01s)
    --- FAIL: TestScript/mod_invalid_version (163.83s)
        script_test.go:260: 
            # Regression test for golang.org/issue/27173: if the user (or go.mod file)
            # requests a pseudo-version that does not match both the module path and commit
            # metadata, reject it with a helpful error message.
…
            > go mod edit -require github.com/pierrec/lz4@473cd7ce01a1
            > go list -m github.com/pierrec/lz4
            [stdout]
            github.com/pierrec/lz4 v0.0.0-20190131084431-473cd7ce01a1
            > stdout 'github.com/pierrec/lz4 v1.0.2-0.20190131084431-473cd7ce01a1'
            FAIL: testdata/script/mod_invalid_version.txt:186: no match for `(?m)github.com/pierrec/lz4 v1.0.2-0.20190131084431-473cd7ce01a1` found in stdout
            
FAIL
FAIL	cmd/go	228.485s

greplogs -l -e 'github\.com/pierrec/lz4 v0\.0\.0-20190131084431-473cd7ce01a1'
2022-05-07T10:56:06-a131fd1/linux-386-longtest
2022-05-06T17:41:30-091e913/linux-386-longtest
2022-04-18T12:04:50-91b9915/linux-386-longtest
2022-04-15T19:02:54-df08c9a/linux-386-longtest
2021-09-07T21:39:06-dcf3545/linux-386-longtest
2020-04-23T13:46:00-708ac9a/linux-386-longtest

I suspect that either cmd/go or git is missing an error check somewhere on the command that fetches the ancestor tags.

[bcmills]

Given the test timing, this is probably another failure mode of #52545. (It should have a better failure mode, though!)