correct usage of mailbox flag (#3123)

<!-- PR description-->

Bug- incorrect usage of mailbox flag in sanity test

#### Does this PR need a docs update or release note?

- [ ] ✅ Yes, it's included
- [ ] 🕐 Yes, but in a later PR
- [x] ⛔ No

#### Type of change

<!--- Please check the type of change your PR introduces: --->
- [ ] 🌻 Feature
- [x] 🐛 Bugfix
- [ ] 🗺️ Documentation
- [ ] 🤖 Supportability/Tests
- [ ] 💻 CI/Deployment
- [ ] 🧹 Tech Debt/Cleanup

#### Issue(s)

<!-- Can reference multiple issues. Use one of the following "magic words" - "closes, fixes" to auto-close the Github issue. -->
* #<issue>

#### Test Plan

<!-- How will this be tested prior to merging.-->
- [x] 💪 Manual
- [ ] ⚡ Unit test
- [ ] 💚 E2E

.github/workflows/sanity-test.yaml

@@ -109,10 +109,9 @@ jobs:
           AZURE_CLIENT_ID: ${{ secrets.CLIENT_ID }}
           AZURE_CLIENT_SECRET: ${{ secrets.CLIENT_SECRET }}
           AZURE_TENANT_ID: ${{ secrets.TENANT_ID }}
-          CORSO_M365_LOAD_TEST_USER_ID: ${{ secrets.CORSO_M365_LOAD_TEST_USER_ID }}
         run: |
           go run . exchange emails \
-          --mailbox ${{ env.CORSO_M365_TEST_USER_ID }} \
+          --user ${{ env.CORSO_M365_TEST_USER_ID }} \
           --tenant ${{ env.AZURE_TENANT_ID }} \
           --destination Corso_Restore_st_${{ steps.repo-init.outputs.result }} \
           --count 4