Revert System.Threading.Tasks.Extensions to 4.3.0

As per PR review comment. No upper bound so users can update to which
ever version they like, and lower bound reflects the lowest we can support.

Author: dtchepak

CHANGELOG.md

@@ -1,7 +1,6 @@
 ### 5.1.0 (Sep 2023)
 
 * [DOC] Add clickable headings. Thanks @jheinath! (#729)
-* [UPDATE] Update `System.Threading.Tasks.Extensions` to latest (`4.5.4-*`) as per @Romfos' suggestion. (#731)
 * [UPDATE] Update `Castle.Core` to `5.1.1-*` to support C# 9 covariants. Thanks @siblount to tracking this down. (#730)
 * [UPDATE] Improved support for testing `ILogger`. Thanks to @zlangner for this contribution, and also thanks to @Saibamen for reviewing this PR. (#732)
 * [NEW] Add `Arg.AnyType` for matching calls with generic parameters. Thanks @icalvo for implementing and documenting this! (#634, #715, #733)

src/NSubstitute/NSubstitute.csproj

@@ -25,7 +25,7 @@
   </ItemGroup>
 
   <ItemGroup Condition="'$(TargetIsNet5OrNewer)' != 'true'">
-    <PackageReference Include="System.Threading.Tasks.Extensions" Version="4.5.4-*" />
+    <PackageReference Include="System.Threading.Tasks.Extensions" Version="4.3.0-*" />
   </ItemGroup>
 
   <PropertyGroup>