Update git-diff-source.md

Example is not valid yaml

Author: agoalofalife

docs/sources/git-diff-source.md

@@ -16,7 +16,7 @@ documents:
           - vendor
         path: src
         contains: class
-        notContains: @deprecated
+        notContains: "@deprecated"
         render:
           strategy: llm
           showStats: true
@@ -188,4 +188,4 @@ documents:
         repository: .
         commit: date:2023-01-15
         filePattern: "*.php"
-```
+```