- Add .NET 9.0 to nuspec

- Update nuspec tags, docs link

EasyPost.nuspec

@@ -9,8 +9,8 @@
         <projectUrl>https://www.easypost.com</projectUrl>
         <license type="expression">MIT</license>
         <requireLicenseAcceptance>false</requireLicenseAcceptance>
-        <description>EasyPost Shipping API Client Library for .NET https://easypost.com/docs</description>
-        <tags>EasyPost ShippingAPI USPS UPS FedEx</tags>
+        <description>EasyPost Shipping API Client Library for .NET https://docs.easypost.com</description>
+        <tags>EasyPost shipping API USPS UPS FedEx DHL CanadaPost RoyalMail mail package logistics rate insurance</tags>
         <readme>docs\README.md</readme>
         <releaseNotes>See Release Notes at https://github.com/EasyPost/easypost-csharp/releases</releaseNotes>
         <icon>images\icon.png</icon>
@@ -27,6 +27,9 @@
             <group targetFramework="net8.0">
                 <dependency id="Newtonsoft.Json" version="[13.0.1, 14.0.0)" />
             </group>
+            <group targetFramework="net9.0">
+                <dependency id="Newtonsoft.Json" version="[13.0.1, 14.0.0)" />
+            </group>
         </dependencies>
     </metadata>
     <files>
@@ -38,6 +41,8 @@
         <file src="lib\net\net7.0\EasyPost.XML" target="lib\net7.0" />
         <file src="lib\net\net8.0\EasyPost.dll" target="lib\net8.0" />
         <file src="lib\net\net8.0\EasyPost.XML" target="lib\net8.0" />
+        <file src="lib\net\net9.0\EasyPost.dll" target="lib\net9.0" />
+        <file src="lib\net\net9.0\EasyPost.XML" target="lib\net9.0" />
         <file src="README.md" target="docs\" />
         <file src="icon.png" target="images\" />
     </files>