Update verify.yml

Author: DilumAluthge

.github/workflows/verify.yml

@@ -22,6 +22,8 @@ jobs:
       - uses: actions/checkout@v2
         with:
           persist-credentials: false
+      - name: Install dependencies (shyaml)
+        run: pip install shyaml
       - run: |
           git clone https://github.com/staticfloat/cryptic-buildkite-plugin.git
           cd cryptic-buildkite-plugin