Credential Loader Test

We have implemented all credential loader that we need for a new release, the only thing left is to test our credential loader to ensure they work as expected.

## Tasks

- [ ] aliyun
- [ ] assume_role_with_oidc
- [ ] default
- [ ] env
- [ ] static
- [x] aws
- [x] assume_role
- [x] assume_role_with_web_identity
- [x] cognito
- [x] default
- [x] ecs
- [x] env
- [x] imds
- [x] process
- [x] profile
- [x] sso
- [x] static
- [x] https://github.com/Xuanwo/reqsign/issues/594
- [x] azure
- [x] azure_cli
- [x] azure_pipeline
- [x] client_certificate
- [x] client_secret
- [x] env
- [x] imds
- [x] static
- [x] workload_identity
- [x] google
- [x] authorized_user
- [x] default
- [x] external_account
- [x] impersonated_service_account
- [x] static_provider
- [x] vm_metadata
- [ ] huaweicloud
- [ ] config
- [ ] default
- [ ] env
- [ ] static
- [ ] tencent
- [ ] assume_role_with_web_identity
- [ ] default
- [ ] env
- [ ] static

No files or test entry points are named. Start by finding the existing tests for the completed AWS, Azure, and Google credential loaders, then follow their conventions for the unchecked Aliyun, HuaweiCloud, and Tencent cases. Done means those listed loaders have coverage and the relevant test suite passes.

Written by the indexing model from the issue text.