chore: Update to cfn-model 0.6.9

[orien]

We should be able to get a passing CI build once Rubygems is upgraded to latest:

--- a/.github/workflows/tests-linting.yml
+++ b/.github/workflows/tests-linting.yml
@@ -28,6 +28,7 @@ jobs:
       uses: ruby/setup-ruby@v1
       with:
         ruby-version: ${{ matrix.ruby }}
+        rubygems: latest
         bundler-cache: true
     - name: Rubocop lint
       run: bundle exec rubocop -D
@@ -51,5 +52,6 @@ jobs:
       uses: ruby/setup-ruby@v1
       with:
         ruby-version: ${{ matrix.ruby }}
+        rubygems: latest
     - name: e2e
       run: bash ./scripts/setup_and_run_end_to_end_tests.sh

There seems to be an incompatibility with older versions of Rubygems and psych version 4.

[orien]

Hi @arothian, is there anything I can help with to get this released?