Browser test failed to run after moving to esm

[MaryGao]

for pr azure-sdk/azure-sdk-for-js#9226 which is generated as esm and we failed to run browser testing.

$ rushx unit-test:browser
Found configuration in D:\test\azure-sdk-for-js\rush.json

Rush Multi-Project Build Tool 5.112.1 - Node.js 18.19.0 (LTS)
> "npm run build:test && dev-tool run test:vitest --no-test-proxy --browser"


> @azure-rest/defender-easm-rest@1.0.0-beta.1 build:test
> npm run clean && tshy && dev-tool run build-test


> @azure-rest/defender-easm-rest@1.0.0-beta.1 clean
> rimraf --glob dist dist-browser dist-esm test-dist temp types *.tgz *.log

[build-test] The file tsconfig.browser.config.json does not exist.
[dev-tool] Errors occured. See the output above.
Error: Failed calling npm run build:test && dev-tool run test:vitest --no-test-proxy --browser.  Exit code: 1

[MaryGao]

see core's change here: https://github.com/Azure/azure-sdk-for-js/pull/26238/files