crypto/x509: replace os.MkdirTemp with T.TempDir

Updates #45402

Change-Id: Ifb1fa5232a0fa1be62e886643cec9deaa3b312ad
Reviewed-on: https://go-review.googlesource.com/c/go/+/308409
Reviewed-by: Ian Lance Taylor <[email protected]>
Reviewed-by: Emmanuel Odeke <[email protected]>

Author: ianwoolf

src/crypto/x509/root_unix_test.go

@@ -147,11 +147,7 @@ func TestLoadSystemCertsLoadColonSeparatedDirs(t *testing.T) {
 		os.Setenv(certFileEnv, origFile)
 	}()
 
-	tmpDir, err := os.MkdirTemp(os.TempDir(), "x509-issue35325")
-	if err != nil {
-		t.Fatalf("Failed to create temporary directory: %v", err)
-	}
-	defer os.RemoveAll(tmpDir)
+	tmpDir := t.TempDir()
 
 	rootPEMs := []string{
 		geoTrustRoot,