Fix: Add version constraints to schemaregistry dependencies (#2007)

This commit adds explicit version constraints to attrs and cachetools
to ensure they are properly installed when using the schemaregistry extra.
This fixes the "No module named 'attrs'" error reported in issue #1972.

The version constraints are based on the versions that were successfully
resolved in the user's pip-compile output.

Co-authored-by: Robert Yokota <[email protected]>

Author: aywengo

requirements/requirements-schemaregistry.txt

@@ -1,4 +1,4 @@
-attrs
-cachetools
+attrs>=21.2.0
+cachetools>=5.5.0
 httpx>=0.26
 authlib>=1.0.0