fix: resolve Rust 1.90.0 compatibility issue with TOKEN_USER handling

[kingsword09]

Fixes STATUS_ACCESS_VIOLATION (exit code 0xc0000005) that occurs when running tests with Rust 1.90.0+.

The issue was discovered through OpenDAL's CI failure:

• Reference: https://github.com/apache/opendal/actions/runs/18054308829/job/51381863340
• The tests pass on Rust 1.89.0 but fail on Rust 1.90.0

[kingsword09]

cc @ho-229

[ho-229]

LGTM