test(cpp): read concore.params from in1/ in the tryparam list test - #676

Problem: the "tryparam preserves list with comma" test in TestConcoreHpp.cpp writes in/1/concore.params, but Concore::load_params() reads <inpath>1/concore.params, i.e. in1/concore.params (the other tests in the file also use in1/). The test therefore never finds its file, and two checks (tryparam preserves list with comma, tryparam preserves subsequent key) fail, which turns the C++ CI jobs red.

Change: write and remove the params file at in1/concore.params. No library code changes.

Testing: g++ -std=c++11 -Wall -Wextra -I. -o TestConcoreHpp TestConcoreHpp.cpp && ./TestConcoreHpp goes from 34 passed, 2 failed to 36 passed, 0 failed (checked on macOS and Linux).