C#: Fix global.json and packages.config lookup

Author: tamasvajk

csharp/extractor/Semmle.Extraction.CSharp.DependencyFetching/DotNet.cs

@@ -143,7 +143,7 @@ private static BuildScript DownloadDotNet(IBuildActions actions, ILogger logger,
             // See https://docs.microsoft.com/en-us/dotnet/core/tools/global-json
             var versions = new List<string>();
 
-            foreach (var path in files.Where(p => p.EndsWith("global.json", StringComparison.Ordinal)))
+            foreach (var path in files.Where(p => p.EndsWith(Path.DirectorySeparatorChar + "global.json", StringComparison.Ordinal)))
             {
                 try
                 {

csharp/extractor/Semmle.Extraction.CSharp.DependencyFetching/FileContent.cs

@@ -184,7 +184,7 @@ private void DoInitialize()
             {
                 try
                 {
-                    var isPackagesConfig = file.EndsWith("packages.config", StringComparison.OrdinalIgnoreCase);
+                    var isPackagesConfig = file.EndsWith(Path.DirectorySeparatorChar + "packages.config", StringComparison.OrdinalIgnoreCase);
 
                     foreach (ReadOnlySpan<char> line in unsafeFileReader.ReadLines(file))
                     {