fix: use isinstance check instead of type (#1411)

[keetonian]

Issue #, if available:
aws-cloudformation/cfn-lint#1325

Description of changes:
Do a correct type check, which will fix a recent SAM bug in cfn-lint

Description of how you validated changes:
make pr

Checklist:

• Write/update tests
• make pr passes
• Update documentation
• Verify transformed template deploys and application functions as expected
• Add/update example to examples/2016-10-31

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

[codecov-io]

Codecov Report

Merging #1449 into release/v1.21.0 will not change coverage.
The diff coverage is 100%.

@@               Coverage Diff                @@
##           release/v1.21.0    #1449   +/-   ##
================================================
  Coverage            94.38%   94.38%           
================================================
  Files                   78       78           
  Lines                 4683     4683           
  Branches               938      938           
================================================
  Hits                  4420     4420           
  Misses                 121      121           
  Partials               142      142

Impacted Files	Coverage Δ
samtranslator/translator/translator.py	98.38% <100%> (ø)	⬆️

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