cmd/go: unexpected TestScript/get_brace timeout on illumos-amd64-joyent

[bcmills]

From the illumos-amd64-joyent builder in https://build.golang.org/log/e8f2fee14aa5f386edc64b79dfeba4f092088200:

go test proxy running at GOPROXY=http://127.0.0.1:38179/mod
--- FAIL: TestScript (0.00s)
    --- FAIL: TestScript/get_brace (443.52s)
        script_test.go:191: 
            # Set up some empty repositories. (6.969s)
            # Clone the empty repositories into GOPATH.
            # This tells the Go command where to find them: it takes the place of a user's meta-tag redirector. (0.965s)
            # Commit contents to the repositories. (1.060s)
            # 'go get' should refuse to download or update the confusingly-named repo. (434.441s)
            > cd $GOPATH/src/example.com/foo
            $WORK/gopath/src/example.com/foo
            > ! go get -u 'example.com/{confusing}'
            [stderr]
            package example.com/{confusing}: example.com/{confusing}: invalid import path: malformed import path "example.com/{confusing}": invalid char '{'
            [exit status 1]
            > stderr 'invalid char'
            > ! go get -u example.com/foo
            [signal: interrupt]
            FAIL: testdata/script/get_brace.txt:40: test timed out while running command
            
FAIL
FAIL	cmd/go	522.698s

I have no idea where all that time went; it's not obvious to me whether this is due to a cmd/go bug or an illumos kernel or filesystem bug.