[CI] Remove tests folder before code signing to reduce signing workload (#44800)

<!-- Enter a brief description/summary of your PR here. What does it
fix/what does it change/how was it tested (even manually, if necessary)?
-->
## Summary of the Pull Request
Remove the tests folder before ESRP code signing step to significantly
reduce the number of files being signed.

## Problem
The current code signing process signs **8,148 files**, with
approximately **5,000+ files** coming from the `tests/` directory. These
test files (primarily localized `.resources.dll` files from test
frameworks) do not need to be signed since they are not included in the
final release package.

The excessive file count causes:
- HTTP 429 (Too Many Requests) throttling from ESRP Gateway
- Signing operations getting stuck in "Inprogress" status
- Pipeline timeouts after ~57 minutes
<img width="1173" height="59" alt="image"
src="https://github.com/user-attachments/assets/ab077293-7efd-4ffe-a788-cbb6e72df3a1"
/>
<img width="1527" height="140" alt="image"
src="https://github.com/user-attachments/assets/7828474e-8bcc-471b-acbe-c898cf70bc34"
/>
<img width="1487" height="357" alt="image"
src="https://github.com/user-attachments/assets/2239d178-6e71-4349-a114-7e5216cbd8cf"
/>

Fix: 
Reduce signing time by 10+ minutes
From
<img width="480" height="58" alt="image"
src="https://github.com/user-attachments/assets/fb40e768-5700-4c00-af6b-6b7d9bf40360"
/>

to
<img width="480" height="63" alt="image"
src="https://github.com/user-attachments/assets/b7ab02fb-3616-4c7e-8e83-7d3afcbd1df3"
/>


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## PR Checklist

- [ ] Closes: #xxx
<!-- - [ ] Closes: #yyy (add separate lines for additional resolved
issues) -->
- [ ] **Communication:** I've discussed this with core contributors
already. If the work hasn't been agreed, this work might be rejected
- [ ] **Tests:** Added/updated and all pass
- [ ] **Localization:** All end-user-facing strings can be localized
- [ ] **Dev docs:** Added/updated
- [ ] **New binaries:** Added on the required places
- [ ] [JSON for
signing](https://github.com/microsoft/PowerToys/blob/main/.pipelines/ESRPSigning_core.json)
for new binaries
- [ ] [WXS for
installer](https://github.com/microsoft/PowerToys/blob/main/installer/PowerToysSetup/Product.wxs)
for new binaries and localization folder
- [ ] [YML for CI
pipeline](https://github.com/microsoft/PowerToys/blob/main/.pipelines/ci/templates/build-powertoys-steps.yml)
for new test projects
- [ ] [YML for signed
pipeline](https://github.com/microsoft/PowerToys/blob/main/.pipelines/release.yml)
- [ ] **Documentation updated:** If checked, please file a pull request
on [our docs
repo](https://github.com/MicrosoftDocs/windows-uwp/tree/docs/hub/powertoys)
and link it here: #xxx

<!-- Provide a more detailed description of the PR, other things fixed,
or any additional comments/features here -->
## Detailed Description of the Pull Request / Additional comments

<!-- Describe how you validated the behavior. Add automated tests
wherever possible, but list manual validation steps taken as well -->
## Validation Steps Performed

.pipelines/v2/templates/job-build-project.yml

@@ -504,6 +504,14 @@ jobs:
         Remove-Item -Force -Recurse "$(JobOutputDirectory)/_appx" -ErrorAction:Ignore
       displayName: Re-pack the new CmdPal package after signing
 
+    - pwsh: |
+        $testsPath = "$(Build.SourcesDirectory)/$(BuildPlatform)/$(BuildConfiguration)/tests"
+        if (Test-Path $testsPath) {
+            Remove-Item -Path $testsPath -Recurse -Force
+            Write-Host "Removed tests folder to reduce signing workload: $testsPath"
+        }
+      displayName: Remove tests folder before signing
+
     - template: steps-esrp-signing.yml
       parameters:
         displayName: Sign Core PowerToys