Fix check for dotnet folder in PATH

Copilot prompt:

In #method:'Microsoft.DotNet.Tools.Bootstrapper.DotnetInstaller.ConfigureInstallType':4481-6459 what I meant by removing a folder from the path if it has dotnet in it was that you should check the contents of each folder and if it is a dotnet installation folder then it should be removed from the path.  A simple way to check if it's a dotnet installation folder is if it has a dotnet executable in it.

Author: dsplaisted

src/Installer/dnup/DotnetInstaller.cs

@@ -109,8 +109,9 @@ public void ConfigureInstallType(SdkInstallType installType, string? dotnetRoot
         // Get current PATH
         var path = Environment.GetEnvironmentVariable("PATH", EnvironmentVariableTarget.User) ?? string.Empty;
         var pathEntries = path.Split(Path.PathSeparator, StringSplitOptions.RemoveEmptyEntries).ToList();
-        // Remove all entries containing "dotnet" (case-insensitive)
-        pathEntries = pathEntries.Where(p => !p.Contains("dotnet", StringComparison.OrdinalIgnoreCase)).ToList();
+        string exeName = OperatingSystem.IsWindows() ? "dotnet.exe" : "dotnet";
+        // Remove only actual dotnet installation folders from PATH
+        pathEntries = pathEntries.Where(p => !File.Exists(Path.Combine(p, exeName))).ToList();
 
         switch (installType)
         {