Fix test expectations for server-provided token scheme casing

[Copilot]

PR #106 changed the implementation to preserve server-provided token scheme casing instead of normalizing it. The tests were asserting normalized values, causing failures.

Changes:

• Updated test_get_token_success to expect "bearer" (lowercase, as returned by mock server) instead of "Bearer"
• Updated test_get_token_respects_token_type to expect "DPoP" (mixed case, as returned by mock server) instead of "Dpop"

The tests now correctly validate that the implementation preserves exact server casing for OAuth token schemes.

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[Copilot]

Just as a heads up, I was blocked by some firewall rules while working on your feedback. Expand below for details.

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[anna-singleton-resolver]

already implemented by me - changing the mocked data to have the standard casing for Bearer and fixign the assertion for DPoP instead of changing both assertions