fix: Modify schema name to service key placeholder in Postgres

[lindseysimple]

Fixes app-functions-sdk-go/#1618. Modify schema name to service key placeholder in Postgres.

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Additional details and impacted files

@@          Coverage Diff          @@
##            main    #678   +/-   ##
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  Coverage   0.00%   0.00%           
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  Files          1       1           
  Lines         25      25           
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  Misses        25      25           

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[cloudxxx8]

LGTM