test(atomic): fix script to scope E2E tests (#4554)

## 2 issues fixed:

1. Incorrect Error Handling: When the script detects a file change from
another package (e.g., headless/), it throws an error but does not set
the `testsToRun` variable. This causes the CI to fail.
2. False Positive Detection: The script incorrectly detects changes in
`headless-react` as changes in `headless`, leading to the execution of
all tests unnecessarily.

https://coveord.atlassian.net/browse/KIT-3667

---------

Co-authored-by: developer-experience-bot[bot] <91079284+developer-experience-bot[bot]@users.noreply.github.com>
Co-authored-by: Alex Prudhomme <78121423+alexprudhomme@users.noreply.github.com>

scripts/ci/find-tests.mjs

@@ -92,12 +92,12 @@ function determineTestFilesToRun(changedFiles, testDependencies) {
 
 function ensureIsNotCoveoPackage(file) {
   if (dependsOnCoveoPackage(file)) {
-    throw new Error('Change detected in an different Coveo package.');
+    throw new Error(`Change detected in an different Coveo package: ${file}`);
   }
 }
 
 function dependsOnCoveoPackage(file) {
-  const externalPackages = ['packages/headless', 'packages/bueno'];
+  const externalPackages = ['packages/headless/', 'packages/bueno/'];
   for (const pkg of externalPackages) {
     if (file.includes(pkg)) {
       return true;
@@ -122,4 +122,5 @@ try {
   }
 } catch (error) {
   console.warn(error?.message || error);
+  setOutput(outputName, ''); // Passing an empty string will run all tests.
 }