Remove unsafe assertion from dynamic route screen detection

[KJ21-ENG]

Explanation of Change

This removes an unnecessary type assertion from dynamic-route screen detection. The configured path is already a string, and the existing Set<string> accepts it directly, so the optional lookup, empty-path guard, exact membership test, and navigation behavior stay unchanged.

The only changed file is src/libs/Navigation/helpers/dynamicRoutesUtils/isDynamicRouteScreen.ts.

Fixed Issues

$ #94739
PROPOSAL: #94739 (comment)

Tests

• Target lint, focused TypeScript, formatting, spelling, changed-path, and diff-hygiene checks passed.
• isDynamicRouteScreenTests.ts passed all 9 cases for configured dynamic paths, regular paths, and an absent configuration. A mutation that inverted the Set result was detected by the 8 configured and regular-path cases.
• Exact-head Fork CI passed typecheck, lint, format, React Compiler, Jest, and the aggregate check.

Limitations: there is no explicit empty-path test. The Jest cases do not distinguish this exact membership check from the broader dynamic-suffix helper, although that helper was not substituted. No manual, device, offline, all-platform, or console QA was performed.

• Verify that no errors appear in the JS console

Offline tests

Not applicable. This cleanup changes no requests or offline handling; offline testing was not performed.

QA Steps

On macOS Chrome in staging, sign in and open Settings > Profile > Personal details > Home address > Country. Verify the Country screen opens and the URL ends in /country; refresh the page, then use Back and verify navigation returns to Home address without an unexpected fullscreen or routing state. Open a regular Settings screen and verify its refresh and Back behavior remain normal. Check the JS console for errors. These steps are recommended and have not been performed.

• Verify that no errors appear in the JS console

PR Author Checklist

• I linked the correct issue in the ### Fixed Issues section above
• I wrote clear testing steps that cover the changes made in this PR
  • I added steps for local testing in the Tests section
  • I added steps for the expected offline behavior in the Offline steps section
  • I added steps for Staging and/or Production testing in the QA steps section
  • I added steps to cover failure scenarios (i.e. verify an input displays the correct error message if the entered data is not correct)
  • I turned off my network connection and tested it while offline to ensure it matches the expected behavior (i.e. verify the default avatar icon is displayed if app is offline)
  • I tested this PR with a High Traffic account against the staging or production API to ensure there are no regressions (e.g. long loading states that impact usability).
• I included screenshots or videos for tests on all platforms
• I ran the tests on all platforms & verified they passed on:
  • Android: Native
  • Android: mWeb Chrome
  • iOS: Native
  • iOS: mWeb Safari
  • MacOS: Chrome / Safari
• I verified there are no console errors (if there's a console error not related to the PR, report it or open an issue for it to be fixed)
• I followed proper code patterns (see Reviewing the code)
  • I verified that comments were added to code that is not self explanatory
  • I verified that any new or modified comments were clear, correct English, and explained "why" the code was doing something instead of only explaining "what" the code was doing.
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• If a new code pattern is added I verified it was agreed to be used by multiple Expensify engineers
• I followed the guidelines as stated in the Review Guidelines
• I tested other components that can be impacted by my changes (i.e. if the PR modifies a shared library or component like Avatar, I verified the components using Avatar are working as expected)
• If a new CSS style is added I verified that:
  • A similar style doesn't already exist
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• I added unit tests for any new feature or bug fix in this PR to help automatically prevent regressions in this user flow.
• If the main branch was merged into this PR after a review, I tested again and verified the outcome was still expected according to the Test steps.

Screenshots/Videos

Not applicable. This cleanup has no visual effect, and no screenshots or videos were produced.