x/build/internal/task: TestSyncPrivate failures with `context deadline exceeded` on darwin

[gopherbot]

#!watchflakes
post <- goos == "darwin" && pkg == "golang.org/x/build/internal/task" && test == "TestSyncPrivate" && `context deadline exceeded`

Issue created automatically to collect these failures.

Example (log):

--- FAIL: TestSyncPrivate (81.19s)
    tagx_test.go:599: task Sync go-private master to public: started
    tagx_test.go:599: task Sync go-private master to public: started
    tagx_test.go:621: 2023-11-19 13:53:48.249599 -0800 PST m=+62.498902576	task Sync go-private master to public: LOG: task failed, will retry (1 of 3): git command failed: signal: killed, stderr Cloning into '/tmp/buildlet/tmp/relui-git-clone-1676881493'...
        done.
    tagx_test.go:599: task Sync go-private master to public: started
    sync_private_test.go:37: context deadline exceeded

— watchflakes

[gopherbot]

Found new dashboard test flakes for:

#!watchflakes
default <- pkg == "golang.org/x/build/internal/task" && test == "TestSyncPrivate"

2023-11-19 20:11 darwin-amd64-12_0 build@c3768868 go@06145fe0 x/build/internal/task.TestSyncPrivate (log)

--- FAIL: TestSyncPrivate (81.19s)
    tagx_test.go:599: task Sync go-private master to public: started
    tagx_test.go:599: task Sync go-private master to public: started
    tagx_test.go:621: 2023-11-19 13:53:48.249599 -0800 PST m=+62.498902576	task Sync go-private master to public: LOG: task failed, will retry (1 of 3): git command failed: signal: killed, stderr Cloning into '/tmp/buildlet/tmp/relui-git-clone-1676881493'...
        done.
    tagx_test.go:599: task Sync go-private master to public: started
    sync_private_test.go:37: context deadline exceeded

— watchflakes

[bcmills]

Looks like another failure in the cluster of #63937.

[bcmills]

Duplicate of #64110