test: correctly make test-output.xml paths relative in windows

[yangannyx]

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• I agree to follow the code of conduct that this project follows, as appropriate.
• The changes are appropriately documented (if applicable).
• The changes have sufficient test coverage (if applicable).
• The testsuite passes successfully on my local machine (if applicable).

Summarize your changes:
This PR aims to improve CircleCI parallelization by ensuring that past timings are detectable. The previous sed script was failing on Windows due to discrepancies over the use of backward and forward slash in directory addresses.

Testing
Tested that running the new script for making test paths relative works on a test xml file generated locally using CI=1 yarn test --suite="slow". Verified relative paths were successfully generated on both mac and windows machines.

Windows generated test_output.xml

  <testsuite name="init" timestamp="2024-06-06T22:58:55" tests="6" file="C:\Users\AnnyYang\code\forge\packages\api\core\test\slow\api_spec_slow.ts" time="0.000" failures="0">

test_output.xml after running preview sed

  <testsuite name="init" timestamp="2024-06-06T22:58:55" tests="6" file="C:\Users\AnnyYang\code\forge\packages\api\core\test\slow\api_spec_slow.ts" time="0.000" failures="0">

test_output.xml after running current sed

  <testsuite name="init" timestamp="2024-06-06T22:58:55" tests="6" file="packages\api\core\test\slow\api_spec_slow.ts" time="0.000" failures="0">

[BlackHole1]

LGTM

[yangannyx]

This LGTM

Commit 1: timings not detected because previous CI runs have incorrect path
Commit 2: timing not detected bc commit 1 had a bug with the sed command
Commit 3: timings detected from commit 2