Skip pinned NuGet packages

This lets us use `Version="[1.2.3,)"` syntax which is equivalent to `Version="1.2.3"` to tell Renovate to not update a specific dependency.

Author: martincostello

.github/renovate.json

@@ -35,6 +35,12 @@
       "matchManagers": ["nuget"],
       "addLabels": [".NET"]
     },
+    {
+      "description": ["Skip pinned NuGet package versions"],
+      "matchManagers": ["nuget"],
+      "matchCurrentValue": "^\\[[^,]+,\\)$",
+      "enabled": false
+    },
     {
       "extends": ["monorepo:dotnet"],
       "description": "Disable major version updates for .NET",