all: use T.TempDir to create temporary test directory (#8280)

This commit replaces `os.MkdirTemp` with `t.TempDir` in tests. The
directory created by `t.TempDir` is automatically removed when the test
and all its subtests complete.

Prior to this commit, temporary directory created using `os.MkdirTemp`
needs to be removed manually by calling `os.RemoveAll`, which is omitted
in some tests. The error handling boilerplate e.g.
	defer func() {
		if err := os.RemoveAll(dir); err != nil {
			t.Fatal(err)
		}
	}
is also tedious, but `t.TempDir` handles this for us nicely.

Reference: https://pkg.go.dev/testing#T.TempDir
Signed-off-by: Eng Zer Jun <engzerjun@gmail.com>

lib/model/sharedpullerstate_test.go

@@ -17,8 +17,7 @@ import (
 // Test creating temporary file inside read-only directory
 func TestReadOnlyDir(t *testing.T) {
 	// Create a read only directory, clean it up afterwards.
-	tmpDir := createTmpDir()
-	defer os.RemoveAll(tmpDir)
+	tmpDir := t.TempDir()
 	if err := os.Chmod(tmpDir, 0555); err != nil {
 		t.Fatal(err)
 	}