Rename the misnamed NUnit VerifyBase.ThrowsValueTask<T> overload (#1886)

VerifyBase declared ThrowsValueTask<T>(Func<Task<T>>), which forwards to
Verifier.ThrowsTask. The name was a copy paste error: the static API and
MSTest's VerifyBase both call this ThrowsTask<T>.

So NUnit's VerifyBase had no generic ThrowsTask at all, and ThrowsValueTask was
overloaded across unrelated Task<T> and ValueTask<T> signatures. Code moved
between the static and instance APIs, or from MSTest, did not compile against
the name it expected.

Renamed rather than kept alongside an obsolete forwarder, since a forwarder
would preserve the overload confusion that is the actual problem here. Callers
of the old name change to ThrowsTask, which is the method they were already
reaching.

Author: SimonCropp

src/Verify.NUnit/VerifyBase_Throws.cs

@@ -24,7 +24,7 @@ public SettingsTask ThrowsTask(
         Verifier.ThrowsTask(target, settings ?? this.settings, sourceFile, lineNumber);
 
     [Pure]
-    public SettingsTask ThrowsValueTask<T>(
+    public SettingsTask ThrowsTask<T>(
         Func<Task<T>> target,
         VerifySettings? settings = null,
         [CallerLineNumber] int lineNumber = 0) =>