Fix ZipHelperTests CI failure by removing fragile directory traversal

[liliankasem]

Summary

Fixes ZipHelperTests.CreateZip_Succeeds failing on certain Windows CI agents with:

System.UnauthorizedAccessException: Access to the path 'C:\Users\cloudtest\Application Data' is denied.

Problem

The test located ZippedExe.csproj by walking up exactly 4 parent directories from the CWD, then doing a recursive GetFiles search from there. This approach had two issues:

1. Fragile depth assumption — the 4-parent walk assumes a specific output directory depth (out/bin/Azure.Functions.Cli.UnitTests/debug/), which could break if the build layout changes.
2. Unsafe recursive enumeration — searching from the repo root with SearchOption.AllDirectories traverses the entire directory tree, including protected Windows junction points (e.g., Application Data → AppData\Roaming) that throw UnauthorizedAccessException.

Fix

Replaced both the hardcoded parent traversal and recursive search with:

• Walk up to repo root reliably by searching for Azure.Functions.Cli.sln as a root marker — works regardless of output directory depth.
• Use the known path directly (test/ZippedExe/) instead of recursively scanning — ZippedExe.csproj is always at a fixed location relative to the repo root.
• Compute outPath from repo root instead of relative .. navigation from the csproj directory.

No recursive directory enumeration of unknown trees is performed anymore.

Changes

• test/Cli/Func.UnitTests/HelperTests/ZipHelperTests.cs — refactored BuildAndCopyFileToZipAsync to find repo root deterministically