Raise an exception if using amp_level with native amp_backend

[rohitgr7]

What does this PR do?

Fixes #9739

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[codecov]

Codecov Report

Merging #9755 (2e9fa59) into master (0d3325e) will increase coverage by 0%.
The diff coverage is 100%.

❗ Current head 2e9fa59 differs from pull request most recent head 382c196. Consider uploading reports for the commit 382c196 to get more accurate results

@@          Coverage Diff           @@
##           master   #9755   +/-   ##
======================================
  Coverage      93%     93%           
======================================
  Files         177     177           
  Lines       15460   15464    +4     
======================================
+ Hits        14317   14321    +4     
  Misses       1143    1143           

[tchaton]

LGMT !