build: Pin MyPY due to internal error

Currently all PRs are failing on an INTERNAL ERROR in MyPY that seems to
have been introduced in 1.12.0. This pins edx-platform to <1.12.0 until
we can find out more information and hopefully get an upstream fix.

Author: bmtcril

requirements/constraints.txt

@@ -123,6 +123,12 @@ markdown<3.4.0
 # Issue for unpinning: https://github.com/openedx/edx-platform/issues/35270
 moto<5.0
 
+# Date: 2024-10-16
+# MyPY 1.12.0 fails on all PRs with the following error:
+# openedx/core/djangoapps/content_libraries/api.py:732: error: INTERNAL ERROR
+# Issue for unpinning: https://github.com/openedx/edx-platform/issues/35667
+mypy<1.12.0
+
 # Date: 2024-07-16
 # We need to upgrade the version of elasticsearch to atleast 7.15 before we can upgrade to Numpy 2.0.0
 # Otherwise we see a failure while running the following command: