DM-40032: Use modernized find_outside_stacklevel for S3 flush warning

[timj]

Requires lsst/utils#167

Checklist

• ran Jenkins
• added a release note for user-visible changes to doc/changes

[codecov]

Codecov Report

Patch and project coverage have no change.

Comparison is base (48fba50) 85.86% compared to head (28645dd) 85.86%.

❗ Current head 28645dd differs from pull request most recent head 3c1c717. Consider uploading reports for the commit 3c1c717 to get more accurate results

Additional details and impacted files

@@           Coverage Diff           @@
##             main      #62   +/-   ##
=======================================
  Coverage   85.86%   85.86%           
=======================================
  Files          27       27           
  Lines        3913     3913           
  Branches      801      801           
=======================================
  Hits         3360     3360           
  Misses        433      433           
  Partials      120      120           

Files Changed	Coverage Δ
...st/resources/_resourceHandles/_s3ResourceHandle.py	81.01% <ø> (ø)

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