test(core): enable no-floating-promises rule for tests (#11915)

Sometimes, missing `await` in the test code can cause timing issues, leading to test failures. This PR enables the `no-floating-promises` rule for the test code to ensure that such errors do not occur.

packages/backend/server/src/__tests__/e2e/test.ts

@@ -6,6 +6,6 @@ export const e2e = test;
 // @ts-expect-error created in prelude.ts
 export const app: TestingApp = globalThis.app;
 
-registerCompletionHandler(() => {
-  app.close();
+registerCompletionHandler(async () => {
+  await app.close();
 });

packages/backend/server/src/__tests__/e2e/workspace/invite.spec.ts

@@ -77,7 +77,7 @@ e2e('should leave a workspace', async t => {
     userId: u2.id,
   });
 
-  app.switchUser(u2.id);
+  await app.switchUser(u2.id);
   const { leaveWorkspace } = await app.gql({
     query: leaveWorkspaceMutation,
     variables: {
@@ -182,7 +182,7 @@ e2e('should invite a user by link', async t => {
     },
   });
 
-  app.switchUser(u2);
+  await app.switchUser(u2);
   const accept = await app.gql({
     query: acceptInviteByInviteIdMutation,
     variables: {
@@ -192,7 +192,7 @@ e2e('should invite a user by link', async t => {
   });
   t.true(accept.acceptInviteById, 'failed to accept invite');
 
-  app.switchUser(owner);
+  await app.switchUser(owner);
   const invite2 = await app.gql({
     query: inviteByEmailMutation,
     variables: {
@@ -233,7 +233,7 @@ e2e('should send invitation notification and leave email', async t => {
   t.is(invitationNotification.payload.inviterId, owner.id);
   t.is(invitationNotification.payload.inviteId, invite.invite);
 
-  app.switchUser(u2);
+  await app.switchUser(u2);
   const accept = await app.gql({
     query: acceptInviteByInviteIdMutation,
     variables: {