test: use T.TempDir to create temporary test directory

[Juneezee]

Related Issues

Proposed Changes

A testing cleanup.

This pull request replaces ioutil.TempDir with t.TempDir. We can use the T.TempDir function from the testing package to create temporary directory. The directory created by T.TempDir is automatically removed when the test and all its subtests complete.

This saves us at least 2 lines (error check, and cleanup) on every instance, or in some cases adds cleanup that we forgot.

func TestFoo(t *testing.T) {
	// before
	tmpDir, err := ioutil.TempDir("", "")
	assert.NoError(t, err)
	defer os.RemoveAll(tmpDir)

	// now
	tmpDir := t.TempDir()
}

Additional Info

https://pkg.go.dev/testing#T.TempDir

Checklist

Before you mark the PR ready for review, please make sure that:

• All commits have a clear commit message.
• The PR title is in the form of of <PR type>: <#issue number> <area>: <change being made>
  • example: fix: #1234 mempool: Introduce a cache for valid signatures
  • PR type: fix, feat, INTERFACE BREAKING CHANGE, CONSENSUS BREAKING, build, chore, ci, docs, misc, perf, refactor, revert, style, test
  • area: venus, venus-messager, venus-miner, venus-gateway, venus-auth, venus-market, venus-sealer, venus-wallet, venus-cluster, api, chain, state, vm, data transfer, mempool, message, block production, multisig, networking, paychan, proving, sealing, wallet
• This PR has tests for new functionality or change in behaviour
• If new user-facing features are introduced, clear usage guidelines and / or documentation updates should be included in venus docs or Discussion Tutorials.
• CI is green

[simlecode]

Thanks for the PR!