chore: stop building a RegExp from a raw filesystem path

[MohammedAlkindi]

One test in @aws-cdk/cloud-assembly-api builds a RegExp out of a joined temp path. On Windows the separator is a backslash, so the \U, \A, \L and \T in a path like C:\Users\...\AppData\Local\Temp are read as identity escapes and those backslashes are silently dropped. The pattern then matches nothing and the test fails on every Windows checkout, while jest still prints the intact-looking path, so the cause is not obvious from the output.

Raising it now because of #1772 and the opt-in Windows integ-test label added in #1957. Comparing the prefix as a plain string removes the class of bug rather than escaping around it.

Running this package's jest on Windows goes from 2 failed, 84 passed to 1 failed, 85 passed. The remaining failure, assembly with tree metadata having no file property specified, is there before and after and is unrelated to this change.

• Unit tests added/updated
• Integration tests added/updated (not applicable, test-only change)

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

[codecov-commenter]

Codecov Report

✅ All modified and coverable lines are covered by tests.
✅ Project coverage is 91.32%. Comparing base (a73eebf) to head (8163a2c).
⚠️ Report is 9 commits behind head on main.

Additional details and impacted files

@@           Coverage Diff           @@
##             main    #1964   +/-   ##
=======================================
  Coverage   91.32%   91.32%           
=======================================
  Files          79       79           
  Lines       12217    12217           
  Branches     1724     1724           
=======================================
  Hits        11157    11157           
  Misses       1025     1025           
  Partials       35       35           

Flag	Coverage Δ
suite.unit	91.32% <ø> (ø)

Flags with carried forward coverage won't be shown. Click here to find out more.

☔ View full report in Codecov by Harness.
📢 Have feedback on the report? Share it here.

🚀 New features to boost your workflow:

• ❄️ Test Analytics: Detect flaky tests, report on failures, and find test suite problems.
• 📦 JS Bundle Analysis: Save yourself from yourself by tracking and limiting bundle sizes in JS merges.