Upgrade test project to .NET 6, upgrade NuGet dependencies, remove .NET 4.5 support

Author: paulirwin

src/F23.StringSimilarity/F23.StringSimilarity.csproj

@@ -1,7 +1,7 @@
 <Project Sdk="Microsoft.NET.Sdk">
 
   <PropertyGroup>
-    <TargetFrameworks>netstandard2.0;net45</TargetFrameworks>
+    <TargetFrameworks>netstandard2.0</TargetFrameworks>
     <PackageId>F23.StringSimilarity</PackageId>
     <PackageVersion>4.1.0</PackageVersion>
     <PackageTags>string;similarity;distance;levenshtein;jaro-winkler;lcs;cosine</PackageTags>
@@ -21,7 +21,7 @@
   </PropertyGroup>
 
   <ItemGroup>
-    <PackageReference Include="Microsoft.SourceLink.GitHub" Version="1.0.0" PrivateAssets="All" />
+    <PackageReference Include="Microsoft.SourceLink.GitHub" Version="1.1.1" PrivateAssets="All" />
   </ItemGroup>
 
   <ItemGroup>

test/F23.StringSimilarity.Tests/F23.StringSimilarity.Tests.csproj

@@ -1,7 +1,7 @@
 <Project Sdk="Microsoft.NET.Sdk">
 
   <PropertyGroup>
-    <TargetFramework>netcoreapp3.1</TargetFramework>
+    <TargetFramework>net6.0</TargetFramework>
   </PropertyGroup>
 
   <ItemGroup>
@@ -15,9 +15,9 @@
   </ItemGroup>
 
   <ItemGroup>
-    <PackageReference Include="Microsoft.NET.Test.Sdk" Version="15.8.0" />
-    <PackageReference Include="xunit" Version="2.4.0" />
-    <PackageReference Include="xunit.runner.visualstudio" Version="2.4.0">
+    <PackageReference Include="Microsoft.NET.Test.Sdk" Version="17.1.0" />
+    <PackageReference Include="xunit" Version="2.4.1" />
+    <PackageReference Include="xunit.runner.visualstudio" Version="2.4.3">
       <PrivateAssets>all</PrivateAssets>
       <IncludeAssets>runtime; build; native; contentfiles; analyzers</IncludeAssets>
     </PackageReference>