[Python] Fix RDF Pythonization tests with builtin_llvm=OFF

On my machine, the RDF pythonization tests don't run when I build ROOT
with `builtin_llvm=OFF`. There is a crash unless I do `import numba` in
the beginning.

I guess it's not a priority to understand the underlying problem because
not many people build ROOT like this and the workaround is easy, but at
least the tests should be green.

We do the same "magically ordered imports" also in other Python tests
where ROOT doesn't work together with xgboost because of `std::regexp`
symbol clashes, unless you do the import in a certain order:

#15183

Author: guitargeek

bindings/pyroot/pythonizations/test/rdf_define_pyz.py

@@ -1,6 +1,12 @@
 import unittest
-import ROOT
+
+import numba  # noqa: F401
 import numpy as np
+import ROOT
+
+# numba is not used directly, but tests can crash when ROOT is built with
+# builtin_llvm=OFF and numba is not imported at the beginning:
+
 
 class PyDefine(unittest.TestCase):
     """

bindings/pyroot/pythonizations/test/rdf_filter_pyz.py

@@ -1,9 +1,14 @@
+import os
 import unittest
-import ROOT
+
+import numba  # noqa: F401
 import numpy as np
+import ROOT
+from rdf_filter_pyz_helper import TYPE_TO_SYMBOL, CreateData, filter_dict
+
+# numba is not used directly, but tests can crash when ROOT is built with
+# builtin_llvm=OFF and numba is not imported at the beginning:
 
-import os
-from rdf_filter_pyz_helper import CreateData, TYPE_TO_SYMBOL, filter_dict
 
 
 class PyFilter(unittest.TestCase):