Fix escaping for Lambda invocation that selects which account to run integration tests in

[ashovlin]

Issue #, if available: N/A

Description of changes: Same as awslabs/aws-dotnet-messaging#94, I'm still not sure what changed that led to this but fixing it up.

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[codecov]

Codecov Report

All modified and coverable lines are covered by tests ✅

Project coverage is 32.34%. Comparing base (74bb0e8) to head (22c6e5a).
Report is 1 commits behind head on dev.

Additional details and impacted files

@@           Coverage Diff           @@
##              dev     #815   +/-   ##
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  Coverage   32.34%   32.34%           
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  Files         271      271           
  Lines       10604    10604           
  Branches     1474     1474           
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  Hits         3430     3430           
  Misses       6885     6885           
  Partials      289      289           

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[ashovlin]

Now the tests are running, but the CI is failing for a different reason. Looks like the version of CDK the Blazor recipe is using is attempting to deploy a Node 14 Lambda which is no longer supported. We'll look at upgrading the CDK dependency in another PR.