chore(dynamodb): migrate tests to assertions (#18560)

Depends on #18577 

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*By submitting this pull request, I confirm that my contribution is made under the terms of the Apache-2.0 license*

Author: robertd

packages/@aws-cdk/aws-dynamodb/package.json

@@ -79,7 +79,7 @@
   },
   "license": "Apache-2.0",
   "devDependencies": {
-    "@aws-cdk/assert-internal": "0.0.0",
+    "@aws-cdk/assertions": "0.0.0",
     "@aws-cdk/cdk-build-tools": "0.0.0",
     "@aws-cdk/cdk-integ-tools": "0.0.0",
     "@aws-cdk/cfn2ts": "0.0.0",