os: TestRootConcurrentClose fails when runtime.AddCleanup is used

[cagedmantis]

While in the process of replacing the use of runtime.SetFinalizer with runtime.AddCleanup (#70907) in the os package, the TestRootConcurrentClose tests started failing. An investigation into the build error on go.dev/cl/638555 showed that on the gotip-wasip1-wasm_wazero builder, TestRootConcurrentClose fails because the goroutine that is spawned runs continuously and never allows the the original function to continue processing.

This seems related to #65178.

@golang/wasm

[gabyhelp]

Related Code Changes

• os: use AddCleanup to close files
• io: use runtime.AddCleanup instead of runtime.SetFinalizer
• net: use runtime.AddCleanup instead of runtime.SetFinalizer

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