Bump System.Text.RegularExpressions from 4.3.0 to 4.3.1

---
updated-dependencies:
- dependency-name: System.Text.RegularExpressions
  dependency-version: 4.3.1
  dependency-type: direct:production
...

Signed-off-by: dependabot[bot] <support@github.com>

Author: dependabot[bot]

WebGoat.NET/WebGoat.NET.csproj

@@ -30,6 +30,7 @@
   </ItemGroup>
 
   <ItemGroup>
+    <PackageReference Include="System.Text.RegularExpressions" Version="4.3.1" />
     <Content Update="wwwroot\css\site.css">
       <CopyToOutputDirectory>PreserveNewest</CopyToOutputDirectory>
     </Content>