Update URLs.

Author: sharpjs

Directory.Build.props

@@ -9,7 +9,7 @@
     * Imported early: this -> NuGet package .props -> SDK .props -> project
     * Many properties are not yet defined and behave as if empty.
     * Provide defaults for properties here.
-    https://docs.microsoft.com/en-us/visualstudio/msbuild/customize-your-build
+    https://learn.microsoft.com/en-us/visualstudio/msbuild/customize-your-build
   -->
 
   <!-- Descriptive properties -->

Directory.Build.targets

@@ -8,7 +8,7 @@
   <!--
     * Imported late: project -> SDK .targets -> NuGet package .targets -> this
     * Override properties and targets here.
-    https://docs.microsoft.com/en-us/visualstudio/msbuild/customize-your-build
+    https://learn.microsoft.com/en-us/visualstudio/msbuild/customize-your-build
   -->
 
   <ItemGroup Condition="'$(IsPackable)' == 'true'">