Fix .NET Framework version mismatch in Snaffler.csproj

Update TargetFrameworkVersion from v4.5.1 to v4.8 to match SnaffCore.csproj.
This resolves the CI build error:

NU1201: Project SnaffCore is not compatible with net451 (.NETFramework,Version=v4.5.1).
Project SnaffCore supports: net48 (.NETFramework,Version=v4.8)

Author: unsu

Snaffler/Snaffler.csproj

@@ -8,7 +8,7 @@
     <OutputType>Exe</OutputType>
     <RootNamespace>Snaffler</RootNamespace>
     <AssemblyName>Snaffler</AssemblyName>
-    <TargetFrameworkVersion>v4.5.1</TargetFrameworkVersion>
+    <TargetFrameworkVersion>v4.8</TargetFrameworkVersion>
     <FileAlignment>512</FileAlignment>
     <Deterministic>true</Deterministic>
     <TargetFrameworkProfile />