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/fs/casefs_test.go

@@ -9,7 +9,6 @@ package fs
 import (
 	"errors"
 	"fmt"
-	"os"
 	"path/filepath"
 	"runtime"
 	"sort"
@@ -28,8 +27,7 @@ func TestRealCase(t *testing.T) {
 		testRealCase(t, newFakeFilesystem(t.Name()+"?insens=true"))
 	})
 	t.Run("actual", func(t *testing.T) {
-		fsys, tmpDir := setup(t)
-		defer os.RemoveAll(tmpDir)
+		fsys, _ := setup(t)
 		testRealCase(t, fsys)
 	})
 }
@@ -83,8 +81,7 @@ func TestRealCaseSensitive(t *testing.T) {
 		testRealCaseSensitive(t, newFakeFilesystem(t.Name()))
 	})
 	t.Run("actual", func(t *testing.T) {
-		fsys, tmpDir := setup(t)
-		defer os.RemoveAll(tmpDir)
+		fsys, _ := setup(t)
 		testRealCaseSensitive(t, fsys)
 	})
 }
@@ -124,8 +121,7 @@ func TestCaseFSStat(t *testing.T) {
 		testCaseFSStat(t, newFakeFilesystem(t.Name()+"?insens=true"))
 	})
 	t.Run("actual", func(t *testing.T) {
-		fsys, tmpDir := setup(t)
-		defer os.RemoveAll(tmpDir)
+		fsys, _ := setup(t)
 		testCaseFSStat(t, fsys)
 	})
 }