test-path: Set umask explicitly (#8616)

test-path: Set umask explicitly (#8616)

Running `test-path` under an umask such as 027 fails with:

  Assertion '(s.st_mode & S_IRWXO) == 0004' failed at ../src/test/test-path.c:247, function test_path_makedirectory_directorymode(). Aborting.

Looking at directory /tmp/test-path_makedirectory, it was indeed created
with mode 0740, applying the umask to the requested 0744.

Set an explicit umask for this test, to ensure reproducible results.