Update Placeholders (#9969)

* Update 8.0.18.md

* Update 9.0.7.md

Author: victorisr

release-notes/8.0/8.0.18/8.0.18.md

@@ -58,7 +58,7 @@ You need [Visual Studio 17.8](https://visualstudio.microsoft.com) or later to us
 
 ## Feedback
 
-Your feedback is important and appreciated. We've created an issue at [dotnet/core #xxxx](https://github.com/dotnet/core/issues/xxxx) for your questions and comments.
+Your feedback is important and appreciated. We've created an issue at [dotnet/core #9967](https://github.com/dotnet/core/issues/9967) for your questions and comments.
 
 [8.0.412]: 8.0.18.md
 [8.0.315]: 8.0.315.md

release-notes/9.0/9.0.7/9.0.7.md

@@ -57,7 +57,7 @@ You need [Visual Studio 17.12](https://visualstudio.microsoft.com) or later to u
 
 ## Feedback
 
-Your feedback is important and appreciated. We've created an issue at [dotnet/core #xxxx](https://github.com/dotnet/core/issues/xxxx) for your questions and comments.
+Your feedback is important and appreciated. We've created an issue at [dotnet/core #9967](https://github.com/dotnet/core/issues/9967) for your questions and comments.
 
 [9.0.302]: 9.0.7.md
 [9.0.108]: 9.0.108.md