Update session.py

[sfc-gh-mkeller]

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1. What GitHub issue is this PR addressing? Make sure that there is an accompanying issue to your PR.

   I have no Jira for this.

2. Fill out the following pre-review checklist:

   • I am adding a new automated test(s) to verify correctness of my new code
   • I am adding new logging messages
   • I am adding a new telemetry message
   • I am adding new credentials
   • I am adding a new dependency

3. Please describe how your code solves the related issue.

   I got the following warning locally:

   /Users/mkeller/snowflakedb/snowapi-python/venv/lib/python3.8/site-packages/snowflake/snowpark/session.py:1891: DeprecationWarning: The 'warn' method is deprecated, use 'warning' instead
    _logger.warn(
   

   I just quickly wanted to fix this warning

[codecov]

Codecov Report

Merging #971 (cc7dd64) into main (2aac082) will not change coverage.
The diff coverage is 100.00%.

@@           Coverage Diff           @@
##             main     #971   +/-   ##
=======================================
  Coverage   98.37%   98.37%           
=======================================
  Files          51       51           
  Lines        9184     9184           
  Branches     1666     1666           
=======================================
  Hits         9035     9035           
  Misses         59       59           
  Partials       90       90           

Files Changed	Coverage Δ
src/snowflake/snowpark/session.py	98.84% <100.00%> (ø)

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