Downgrade buildless TSP warnings to notes

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

@@ -667,7 +667,7 @@ namespace Semmle.Extraction.CSharp.DependencyFetching
                     "Found unreachable Nuget feed in C# analysis with build-mode 'none'",
                     visibility: new DiagnosticMessage.TspVisibility(statusPage: true, cliSummaryTable: true, telemetry: true),
                     markdownMessage: "Found unreachable Nuget feed in C# analysis with build-mode 'none'. This may cause missing dependencies in the analysis.",
-                    severity: DiagnosticMessage.TspSeverity.Warning
+                    severity: DiagnosticMessage.TspSeverity.Note
                 ));
             }
             compilationInfoContainer.CompilationInfos.Add(("All Nuget feeds reachable", allFeedsReachable ? "1" : "0"));

csharp/ql/integration-tests/posix-only/standalone_dependencies_nuget_config_error_timeout/diagnostics.expected

@@ -28,7 +28,7 @@
 }
 {
   "markdownMessage": "Found unreachable Nuget feed in C# analysis with build-mode 'none'. This may cause missing dependencies in the analysis.",
-  "severity": "warning",
+  "severity": "note",
   "source": {
     "extractorName": "csharp",
     "id": "csharp/autobuilder/buildless/unreachable-feed",

csharp/ql/integration-tests/posix-only/standalone_dependencies_nuget_config_fallback/diagnostics.expected

@@ -28,7 +28,7 @@
 }
 {
   "markdownMessage": "Found unreachable Nuget feed in C# analysis with build-mode 'none'. This may cause missing dependencies in the analysis.",
-  "severity": "warning",
+  "severity": "note",
   "source": {
     "extractorName": "csharp",
     "id": "csharp/autobuilder/buildless/unreachable-feed",