Switch back to tf-nightly package, tracking IREE

We need to use the same version of the package that IREE does at
https://github.com/iree-org/iree/blob/main/integrations/tensorflow/test/requirements.txt

Change-Id: I0398b6d28f271c989284cf5de2a7a89fdedb75f4

python-requirements.txt

diff --git a/python-requirements.txt b/python-requirements.txt
index 07a2fc8..95882a4 100644
--- a/python-requirements.txt
+++ b/python-requirements.txt
@@ -42,6 +42,6 @@
 scipy
 sel4-deps
 setuptools
-tensorflow>=2.16.1
+tf-nightly==2.16.0.dev20240207
 wget
 yapf