test/c_api: don't use database if unecessary

[Riolku]

A small optimization in release mode (but a large optimization in debug mode), we can avoid creating a database in our CApi tests in some cases.

[codecov]

Codecov Report

All modified lines are covered by tests ✅

Comparison is base (b79718b) 89.67% compared to head (ce90d01) 89.68%.

Additional details and impacted files

@@           Coverage Diff           @@
##           master    #2234   +/-   ##
=======================================
  Coverage   89.67%   89.68%           
=======================================
  Files        1008     1008           
  Lines       35830    35830           
=======================================
+ Hits        32131    32133    +2     
+ Misses       3699     3697    -2     

Files	Coverage Δ
src/storage/buffer_manager/vm_region.cpp	86.66% <ø> (ø)

... and 2 files with indirect coverage changes

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