fix: update test to start new 2FA session for invalid backup code check

packages/better-auth/src/plugins/two-factor/two-factor.test.ts

@@ -322,10 +322,30 @@ describe("two factor", async () => {
 		expect(currentBackupCodes.backupCodes).toBeDefined();
 		expect(currentBackupCodes.backupCodes).not.toContain(backupCode);
 
+		// Start a new 2FA session to test invalid backup code
+		const headers2 = new Headers();
+		await client.signIn.email({
+			email: testUser.email,
+			password: testUser.password,
+			fetchOptions: {
+				onSuccess(context) {
+					const parsed = parseSetCookieHeader(
+						context.response.headers.get("Set-Cookie") || "",
+					);
+					headers2.append(
+						"cookie",
+						`better-auth.two_factor=${
+							parsed.get("better-auth.two_factor")?.value
+						}`,
+					);
+				},
+			},
+		});
+
 		const res = await client.twoFactor.verifyBackupCode({
 			code: "invalid-code",
 			fetchOptions: {
-				headers,
+				headers: headers2,
 				onSuccess(context) {
 					const parsed = parseSetCookieHeader(
 						context.response.headers.get("Set-Cookie") || "",