ci(snowflake): allow tests to use WIF auth

[ragesh-g]

resolves N/A

Problem

The integration-tests-snowflake CI job can't authenticate via Workload Identity Federation, blocking the WIF functional test in #1316.

Solution

• Adds id-token: write to the snowflake job so the runner exposes the OIDC env vars (ACTIONS_ID_TOKEN_REQUEST_URL / ACTIONS_ID_TOKEN_REQUEST_TOKEN) to the test process.
• Adds SNOWFLAKE_TEST_WIF_USER env var pointing at a dedicated WIF service user (separate from SNOWFLAKE_TEST_USER because Snowflake WIF requires TYPE = SERVICE, which can't have password auth).

Currently unused. Consumed by #1316; landing first so the consuming PR has the infra it needs (pull_request_target workflows load YAML from main).

Testing

[gw3] [ 50%] PASSED tests/functional/auth_tests/test_workload_identity_federation_oidc.py::TestSnowflakeWorkloadIdentityFederation::test_snowflake_wif_basic_functionality

Ran the test against the PR #1316

Checklist

• I have read the contributing guide and understand what's expected of me
• I have run this code in development and it appears to resolve the stated issue
• This PR includes tests, or tests are not required/relevant for this PR
• This PR has no interface changes (e.g. macros, cli, logs, json artifacts, config files, adapter interface, etc) or this PR has already received feedback and approval from Product or DX