fix: KeyFileTypeServiceAccount not found compile error

[jonyhy96]

Motivation

KeyFileTypeServiceAccount is not defiend in the latest version of oauth2/client_credentials_provider.go file,so there will be a compile error in oauth2/client_credentials_flow_test.go

Modifications

change KeyFileTypeServiceAccount to "resource" in test file.

Verifying this change

• Make sure that the change passes the CI checks.

This change is a trivial rework / code cleanup without any test coverage.

Does this pull request potentially affect one of the following parts:

If yes was chosen, please highlight the changes

• Dependencies (does it add or upgrade a dependency): no
• The public API: no
• The schema: no

Documentation

• Does this pull request introduce a new feature? no