Pin jinja2 in CI (Qiskit#7815)

The recent jinja2 release is breaking the tutorials ci job. This is
because something in the nbsphinx, jupyter, sphinx pipeline is
incompatible with the new version. These issues have been reported
upstream to jinja2 (and promptly closed as won't fix) so until the docs
build toolchain is upgraded to work with the new version this commit
pins the jinja2 version.

constraints.txt

@@ -8,3 +8,8 @@ jsonschema==3.2.0
 # as we won't get matplotlib upgrades by default, this constraint likely can't
 # be removed until we can unpin matplotlib.
 pyparsing<3.0.0
+
+# Jinja2 3.1.0 is incompatible with sphinx and/or jupyter until they are updated
+# to work with the new jinja version (the jinja maintainers aren't going to
+# fix things) pin to the previous working version.
+jinja2==3.0.3