run-unit-test: Pass -blastdb_version 4 to fix tests on 32 bit

The autopkgtests currently fail on 32-bit arches with Error: mdb_env_open: Cannot allocate memory.

I found a similar commit in python-biopython and tried that here, and it works.

I could only try that by editing the test script inside an already failed envrionment though. When I build the package for i386, it fails with config.status:55855: error: flat makefile generation failed. (maybe I should file a bug about that).