fix: add sa-east-1 region back to E2E test pool (#3480)

#### Description of changes

Re-adds `sa-east-1` (São Paulo) region to the E2E test pool.

##### CDK / CloudFormation Parameters Changed

None.

#### Issue #, if available

N/A

#### Description of how you validated changes

- E2E test run in progress (batch
`e0e7fc3a-71e2-43aa-a40b-2dd944d5d768`)

#### Checklist

- [x] PR description included
- [ ] `yarn test` passes
- [ ] E2E test run linked
- [x] Tests are changed or added
- [ ] Relevant documentation is changed or added (and PR referenced)
- [ ] New AWS SDK calls or CloudFormation actions have been added to
relevant test and service IAM policies
- [x] Any CDK or CloudFormation parameter changes are called out
explicitly

By submitting this pull request, I confirm that my contribution is made
under the terms of the Apache 2.0 license.

Author: sarayev