Ensure the existence of DDPPlugin._sync_dir in reconciliate_processes

[yifuwang]

What does this PR do?

Fixes #8938

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[codecov]

Codecov Report

Merging #8939 (7a7aff8) into master (89156b7) will decrease coverage by 4%.
The diff coverage is 50%.

@@           Coverage Diff           @@
##           master   #8939    +/-   ##
=======================================
- Coverage      93%     89%    -4%     
=======================================
  Files         173     173            
  Lines       14182   14184     +2     
=======================================
- Hits        13174   12597   -577     
- Misses       1008    1587   +579     

[ananthsub]

Thanks for the fix!

[tchaton]

Oh interesting !