test: pin charset-normalizer below 3.5.0 to fix Python 3.14 CI failures

charset-normalizer 3.5.0 rewrote its compiled extension from mypyc to
Cython, which is ABI-broken on Python 3.14:

  AttributeError: module 'charset_normalizer.md' has no attribute 'CharInfo'

This was breaking pytest collection (via requests -> charset-normalizer)
on the Python 3.14 test containers (Ubuntu 26.04, Photon OS 5), unrelated
to the bootstrap-salt.sh changes in this branch.

Author: twangboy

tests/requirements.txt

@@ -1,3 +1,7 @@
 pytest
 requests
 packaging
+# charset-normalizer>=3.5.0 rewrote its compiled extension from mypyc to
+# Cython, which is ABI-broken on Python 3.14 (AttributeError:
+# module 'charset_normalizer.md' has no attribute 'CharInfo').
+charset-normalizer<3.5.0