fix: strip whitespace from CODECOV_TOKEN in Authorization header

[sentry]

This PR addresses the InvalidHeader error (CLI-1R) that occurs when the CODECOV_TOKEN environment variable contains trailing whitespace, such as a newline character. This is common when the token is sourced from a CI secret or file.

The requests library rejects header values containing reserved characters like newlines. Previously, the get_token_header and get_token_header_or_fail functions in codecov_cli/helpers/request.py would interpolate the token directly into the Authorization header without sanitization.

This fix modifies both functions to call .strip() on the token before constructing the header. This ensures that any leading or trailing whitespace is removed, preventing the InvalidHeader error. Since Codecov tokens are typically UUIDs and do not legitimately contain surrounding whitespace, this change does not compromise security or functionality.

Fixes CLI-1R