Rename gost2814789t.c to gost2814789test.c. The old name caused problems

for dummytest if gost is compiled out, since the name of the test is not
standard (dummytest segfaults). Also the old name caused problems for git
because the executable was not in the .gitignore file

Reviewed-by: Emilia Käsper <emilia@openssl.org>