## Description
Fixed the attachment placeholder for a query created on SMTP datasource
Fixes#21458
## Type of change
- Bug fix (non-breaking change which fixes an issue)
## How Has This Been Tested?
- Manual
For sending email with attachments, tested `{{FilePicker.files}}` and
`{{[FilePicker.files[0]]}}`, both works successfully but
`{{FilePicker.files[0]}}`
## Checklist:
### Dev activity
- [x] My code follows the style guidelines of this project
- [x] I have performed a self-review of my own code
- [ ] I have commented my code, particularly in hard-to-understand areas
- [ ] I have made corresponding changes to the documentation
- [x] My changes generate no new warnings
- [ ] I have added tests that prove my fix is effective or that my
feature works
- [ ] New and existing unit tests pass locally with my changes
- [ ] PR is being merged under a feature flag
### QA activity:
- [ ] Test plan has been approved by relevant developers
- [ ] Test plan has been peer reviewed by QA
- [ ] Cypress test cases have been added and approved by either SDET or
manual QA
- [ ] Organized project review call with relevant stakeholders after
Round 1/2 of QA
- [ ] Added Test Plan Approved label after reveiwing all Cypress test
b0536861b0