fix: pin es client to 8.18

The `elasticsearch` python client is now installing 9.0.0 by default
which is breaking all the notebook tests. Pinning to 8.18 until we can
update the test code to support the 9.0 client

Author: TattdCodeMonkey

Makefile

@@ -21,4 +21,4 @@ install-pre-commit:
 
 install-nbtest:
 	python3 -m venv $(VENV)
-	$(VENV)/bin/pip install -qqq elastic-nbtest sentence-transformers==2.7.0
+	$(VENV)/bin/pip install -qqq elastic-nbtest sentence-transformers==2.7.0 elasticsearch==8.18.0