fix(ci): unpin boto3 in e2e workflow (aws#841)

The pinned boto3==1.38.0 did not include the bedrock-agentcore-control
service model, causing import-resources e2e tests to fail with
UnknownServiceError. Using latest boto3 ensures new AWS services are
always available.

Author: jesseturner21

.github/workflows/e2e-tests-full.yml

@@ -41,7 +41,7 @@ jobs:
           git config --global user.name "CI"
       - uses: astral-sh/setup-uv@v7
       - name: Install Python dependencies for import tests
-        run: pip install boto3==1.38.0
+        run: pip install boto3
       - name: Configure AWS credentials
         uses: aws-actions/configure-aws-credentials@v6
         with: