Tests: use t.Setenv to set env vars (#69516)

This commit replaces `os.Setenv` with `t.Setenv` in tests. The
environment variable is automatically restored to its original value
when the test and all its subtests complete.

Reference: https://pkg.go.dev/testing#T.Setenv

Signed-off-by: Eng Zer Jun <engzerjun@gmail.com>

pkg/services/provisioning/notifiers/config_reader_test.go

@@ -3,7 +3,6 @@ package notifiers
 import (
 	"context"
 	"fmt"
-	"os"
 	"testing"
 
 	"github.com/stretchr/testify/require"
@@ -70,7 +69,7 @@ func TestNotificationAsConfig(t *testing.T) {
 
 		t.Run("Can read correct properties", func(t *testing.T) {
 			setup()
-			_ = os.Setenv("TEST_VAR", "default")
+			t.Setenv("TEST_VAR", "default")
 			cfgProvider := &configReader{
 				orgService:        orgService,
 				encryptionService: encryptionService,
@@ -78,7 +77,6 @@ func TestNotificationAsConfig(t *testing.T) {
 			}
 
 			cfg, err := cfgProvider.readConfig(context.Background(), correctProperties)
-			_ = os.Unsetenv("TEST_VAR")
 			if err != nil {
 				t.Fatalf("readConfig return an error %v", err)
 			}