Fix k5test minimum version requirement

The test function test_set_password fails when run with k5test 0.10.3.

```
TypeError: MITRealm.start_kadmind() missing 1 required positional argument: 'env'
```

This is because it is running the start_kadmind method with no
arguments, but the env argument didn't become optional until k5test
0.10.4.  That is now the new minimum version for this test dependency.

4cbfe7d
pythongssapi/k5test@aa9cf87

requirements-dev.txt

@@ -1,6 +1,6 @@
 black==22.10.0
 isort==5.10.1
-k5test>=0.10.0
+k5test>=0.10.4
 mypy==0.982
 pre-commit
 pytest