[BUG] `make test` doesn't work with when PROG_SUFFIX is used

[zuiderkwast]

Building with PROG_SUFFIX=-a creates the binaries valkey-server-a, valkey-cli-a, etc.

make PROG_SUFFIX=-a
make test

The tests use hard-coded paths to the binaries without these suffixes, so the tests fail to find the binaries. These tests would need use some variable instead of hard-coded binary names. (This might be partially solved by #2816.)

make test runs the runtest script. The make test rule could pass the prog suffix to that script as an argument.

Original discussion in #2880