protondrive: make the tests honour RCLONE_CONFIG whichever tests run

Only fstest.Initialise, run by the integration test, applied
RCLONE_CONFIG, so a filtered test run read the default rclone config,
which may hold a real Proton remote. TestMain now applies it first.

Co-Authored-By: Claude Opus 5.5 <noreply@anthropic.com>

backend/protondrive/budget_test.go

@@ -11,6 +11,7 @@ import (
 
 	"github.com/rclone/rclone/backend/protondrive/protontest"
 	"github.com/rclone/rclone/fs"
+	"github.com/rclone/rclone/fs/config"
 	"github.com/rclone/rclone/fs/object"
 	"github.com/rclone/rclone/fs/operations"
 	fssync "github.com/rclone/rclone/fs/sync"
@@ -31,7 +32,17 @@ const (
 
 // TestMain runs the tests, then fails the run if any of them, through
 // any fake server, requested a removed share-scoped route.
+//
+// The config file is RCLONE_CONFIG's, as on rclone's command line,
+// whichever tests run: only fstest.Initialise would apply it, so the
+// default config, which may hold a real Proton remote, would be read.
 func TestMain(m *testing.M) {
+	if path, ok := os.LookupEnv("RCLONE_CONFIG"); ok {
+		if err := config.SetConfigPath(path); err != nil {
+			fmt.Fprintf(os.Stderr, "FAIL: RCLONE_CONFIG: %v\n", err)
+			os.Exit(1)
+		}
+	}
 	code := m.Run()
 	if legacy := protontest.LegacyRequests(); len(legacy) > 0 {
 		fmt.Fprintf(os.Stderr, "FAIL: TestBudgetNoLegacyRoutes: removed share-scoped routes were requested: %v\n", legacy)