fix: Constrain xblocks-contrib until it can be updated.

Author: farhan

requirements/constraints.txt

@@ -136,3 +136,7 @@ django-debug-toolbar<6.0.0
 # Issue: https://github.com/openedx/edx-platform/issues/37435
 cryptography<46.0.0
 pact-python<3.0.0
+
+# This pin will be removed once the following PR is merged
+# https://github.com/openedx/xblocks-contrib/pull/120
+xblocks-contrib<0.9.0