[wasm] Fix "we can't find snapshot urls" (dotnet#99814)

* Update snapshot url.

* Remove whitespace.

src/tasks/WasmBuildTasks/UpdateChromeVersions.cs

@@ -271,7 +271,7 @@ private async Task<Stream> GetDownloadFileStreamAsync(string filename, string ur
 
     private async Task<string?> FindSnapshotUrlFromBasePositionAsync(string osPrefix, ChromeVersionSpec version, bool throwIfNotFound = true)
     {
-        string baseUrl = $"{s_snapshotBaseUrl}/{osPrefix}";
+        string baseUrl = $"{s_snapshotBaseUrl}?prefix={osPrefix}";
 
         int branchPosition = int.Parse(version.branch_base_position);
         for (int i = 0; i < MaxBranchPositionsToCheck; i++)