Fix broken "Dockerfiles" search link

The recent .NET 10 PR (microsoft#1271) has a GitHub search link that is reporting a 429 in reviewdog; on closer inspection, I found that it no longer return results, but rather a warning.

I have replaced it with the equivalent search link, but with guidance from microsoft#1175, which fixed a similar link but restricted it to `src/` Dockerfiles.

Note this may not necessarily fix the 429 that reviewdog is getting as there may be other factors causing it.

Author: cdonnellytx

documentation/guiding-principles.md

@@ -28,7 +28,7 @@ See the [supported tags](supported-tags.md) for the tagging practices and polici
 
 1. Images will never be deleted from the [official .NET Framework Docker repositories on the Microsoft Artifact Registry](https://mcr.microsoft.com/catalog?search=dotnet/framework).
 
-1. The [Dockerfiles](https://github.com/microsoft/dotnet-framework-docker/search?q=filename%3ADockerfile) used to produce all of the images will be publicly available. Customers will be able to take the Dockerfiles and build them to produce their own equivalent images.  No special build steps or permissions should be needed to build the Dockerfiles.
+1. The [Dockerfiles](https://github.com/search?q=repo%3Amicrosoft%2Fdotnet-framework-docker+path%3Asrc%2F**%2FDockerfile&type=code) used to produce all of the images will be publicly available. Customers will be able to take the Dockerfiles and build them to produce their own equivalent images.  No special build steps or permissions should be needed to build the Dockerfiles.
 
 1. If a change is ever made to the tagging patterns, all of the old tags will be serviced appropriately through its original lifetime.  All old tags will no longer be documented within the tag details section of the readme.