fix: components/aws/sagemaker/dev_requirements.txt to reduce vulnerabilities

The following vulnerabilities are fixed by pinning transitive dependencies:
- https://snyk.io/vuln/SNYK-PYTHON-PROTOBUF-15090738

Author: snyk-bot

components/aws/sagemaker/dev_requirements.txt

@@ -5,4 +5,5 @@ kfp==1.7.0
 docformatter==1.3.1
 black==19.10b0
 coverage==5.1
-pytest==5.4.1
+pytest==5.4.1
+protobuf>=6.33.5 # not directly required, pinned by Snyk to avoid a vulnerability