Update azure-identity for pylint 4.0.4 compatibility

[Copilot]

azure-identity has a small set of pylint 4.0.4 compatibility issues that will turn into build failures when the repo updates its pinned version. The new warnings were limited to workload identity transport imports and a sample credential implementation.

Automated Fix: This PR was automatically generated by Copilot in response to a vnext compatibility issue.

• Workload identity transport imports

  • Added targeted networking-import-outside-azure-core-transport suppressions on the requests imports used by the token-binding transport implementations.
  • Kept the change local to the intentional transport extension points rather than broadening package-level suppression.

• Sample credential cleanup

  • Updated samples/custom_credentials.py to satisfy pylint 4.0.4 docstring requirements for get_token.
  • Added explicit exception chaining when converting MSAL failures into AuthenticationRequiredError.
  • Normalized import grouping in the sample.

• Scope

  • No changelog, version, formatting, or generated-code updates.
  • No functional library behavior changes beyond the sample’s error propagation being made explicit.

Example of the targeted changes:

from requests import Session  # pylint: disable=networking-import-outside-azure-core-transport

try:
    return AccessToken(result["access_token"], now + int(result["expires_in"]))
except Exception as ex:
    raise AuthenticationRequiredError(scopes) from ex