CI: Don't run poetry update

This causes `poetry` to regenerate the `poetry.lock` file with newer versions
of dependencies, which defeats the point of checking in the lock file in the
first place.

saw-remote-api/scripts/run_rpc_tests.sh

@@ -13,7 +13,6 @@ function run_test {
 }
 
 echo "Setting up python environment for remote server clients..."
-poetry update
 poetry install
 
 echo "Typechecking code with mypy..."