Ignore FluentAssertions in Dependabot config (#16605)

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.github/dependabot.yml

@@ -20,13 +20,15 @@ updates:
       day: "sunday"
     ignore:
       - dependency-name: "Moq"
+      - dependency-name: "FluentAssertions"
   - package-ecosystem: "nuget"
     directory: "/src/vs-bicep"
     schedule:
       interval: "weekly"
       day: "sunday"
     ignore:
       - dependency-name: "Moq"
+      - dependency-name: "FluentAssertions"
       # This causes problems with the mirror build because it tends to pull in Roslyn versions that are incompatible (ADO seems to lag behind the versions used in github actions)
       - dependency-name: "Microsoft.CodeAnalysis.CSharp.CodeStyle"
     labels: