feat(cli): count resources/stacks with UNKNOWN drift status as unchecked

[iankhou]

Fixes #740

The cdk drift action lists UNKNOWN for resources/stacks when CloudFormation returns that value (effective August 14).

This follows a new change in the CloudFormation API. Previously, UNKNOWN was not available, and stacks/resources that fit such a description would have been reported as unchanged.

Brought line coverage for @aws-cdk/toolkit-lib/lib/api/drift to 100%.

• UNKNOWN support
• Unit Test

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[codecov-commenter]

Codecov Report

✅ All modified and coverable lines are covered by tests.
✅ Project coverage is 82.34%. Comparing base (0e27c14) to head (666ad44).

Additional details and impacted files

@@            Coverage Diff             @@
##             main     #747      +/-   ##
==========================================
- Coverage   83.06%   82.34%   -0.73%     
==========================================
  Files          65       65              
  Lines        9509     9509              
  Branches     1123     1108      -15     
==========================================
- Hits         7899     7830      -69     
- Misses       1578     1648      +70     
+ Partials       32       31       -1     

Flag	Coverage Δ
suite.unit	82.34% <ø> (-0.73%)	⬇️

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[mrgrain]

I think from a DX perspective unchecked and unknown are pretty much the same. I propose you just piggy back on unchecked.