Bump DiffEngine to version 18.0.0

Updated the DiffEngine package version from 17.0.2 to 18.0.0 in Directory.Packages.props to use the latest features and fixes.

Author: SimonCropp

src/Directory.Packages.props

@@ -7,7 +7,7 @@
     <PackageVersion Include="Argon" Version="0.33.0" />
     <PackageVersion Include="Argon.FSharp" Version="0.33.0" />
     <PackageVersion Include="BenchmarkDotNet" Version="0.15.8" />
-    <PackageVersion Include="DiffEngine" Version="17.0.2" />
+    <PackageVersion Include="DiffEngine" Version="18.0.0" />
     <PackageVersion Include="Expecto" Version="10.2.3" />
     <PackageVersion Include="Fixie" Version="4.2.0" />
     <PackageVersion Include="Fixie.TestAdapter" Version="4.2.0" />