Cannot authenticate using SSO/Identity Center: "missing required scope: sso:account:access"

## Problem

AWS Toolkit for VSCode fails to use AWS Identity Center SSO

### Log
```
2025-03-08 11:31:59.102 [info] auth: Updating connection state of profile:awsicsso to authenticating
2025-03-08 11:31:59.102 [info] auth: Handling validation error of connection: profile:awsicsso
2025-03-08 11:31:59.102 [info] auth: Updating connection state of profile:awsicsso to invalid
2025-03-08 11:31:59.103 [error] _aws.toolkit.auth.reauthenticate: Error: Unable to authenticate connection
-> Error: Session for "awsicsso" is missing required scope: sso:account:access
```

### Configuration

~/.aws/config (redacted)
```
[sso-session sso]
sso_region = us-east-2
sso_start_url = https://d-123example.awsapps.com/start
sso_registration_scope = sso:account:access

[profile awsicsso]
sso_session = sso
sso_account_id = 123456789012
sso_role_name = DeveloperAccess
region = ca-central-1
output = json
```

## Steps to reproduce the issue

## Expected behavior

Credential is accepted and plugin works

## System details (run `AWS: About` and/or `Amazon Q: About`)

- OS: Darwin x64 24.3.0
- Visual Studio Code version: 1.97.0
- AWS Toolkit version: 3.46.0
- Amazon Q version: N/A

No source file or test is identified in the report. First reproduce with the shown AWS configuration and `aws sts get-caller-identity --profile awsicsso`, then select the profile through the AWS Toolkit connection picker in VSCode and inspect the Output error. Done means the `awsicsso` credential is accepted and the plugin works without the missing-scope error.

Written by the indexing model from the issue text.