Fix incorrect precision="mixed" being used with DeepSpeedStrategy and IPUStrategy

[rohitgr7]

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See title.

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cc @Borda @awaelchli @rohitgr7 @akihironitta @carmocca @justusschock

[codecov]

Codecov Report

Merging #14041 (3b39e93) into master (d29a552) will increase coverage by 15%.
The diff coverage is 67%.

❗ Current head 3b39e93 differs from pull request most recent head d39819e. Consider uploading reports for the commit d39819e to get more accurate results

@@            Coverage Diff            @@
##           master   #14041     +/-   ##
=========================================
+ Coverage      61%      76%    +15%     
=========================================
  Files         324      324             
  Lines       26369    26422     +53     
=========================================
+ Hits        16138    20148   +4010     
+ Misses      10231     6274   -3957     

[rohitgr7]

should this go as a bugfix or main release now?

[Borda]

should this go as a bugfix or main release now?

I would say rather bugfix one