soci: fix build w/glibc-2.34

We don't run the tests and I didn't manage to get them running
trivially, so let's disable them. This not only speeds up
compilation-time, but also fixes the build for glibc 2.34.

Failing Hydra build: https://hydra.nixos.org/build/163952252

pkgs/development/libraries/soci/default.nix

···
   ];
 
   # Do not build static libraries
-  cmakeFlags = [ "-DSOCI_STATIC=OFF" "-DCMAKE_CXX_STANDARD=11" ];
+  cmakeFlags = [ "-DSOCI_STATIC=OFF" "-DCMAKE_CXX_STANDARD=11" "-DSOCI_TESTS=off" ];
 
   nativeBuildInputs = [ cmake ];
   buildInputs = [