Declare new api in net 9 (#3136)

Author: westin-m

src/Microsoft.Identity.Web.TokenAcquisition/PublicAPI/net9.0/InternalAPI.Unshipped.txt

@@ -2,5 +2,6 @@
 Microsoft.Identity.Web.MergedOptions.AppHomeTenantId.get -> string?
 Microsoft.Identity.Web.MergedOptions.AppHomeTenantId.set -> void
 Microsoft.Identity.Web.TokenAcquisitionExtensionOptions.InvokeOnBeforeTokenAcquisitionForApp(Microsoft.Identity.Client.AcquireTokenForClientParameterBuilder! builder, Microsoft.Identity.Abstractions.AcquireTokenOptions? acquireTokenOptions) -> void
+Microsoft.Identity.Web.TokenAcquisitionExtensionOptions.InvokeOnBeforeTokenAcquisitionForTestUser(Microsoft.Identity.Client.AcquireTokenByUsernameAndPasswordConfidentialParameterBuilder! builder, Microsoft.Identity.Abstractions.AcquireTokenOptions? acquireTokenOptions) -> void
 readonly Microsoft.Identity.Web.TokenAcquisition.tokenAcquisitionExtensionOptionsMonitor -> Microsoft.Extensions.Options.IOptionsMonitor<Microsoft.Identity.Web.TokenAcquisitionExtensionOptions!>?
 static Microsoft.Identity.Web.TokenAcquisition.ResolveTenant(string? tenant, Microsoft.Identity.Web.MergedOptions! mergedOptions) -> string?

src/Microsoft.Identity.Web.TokenAcquisition/PublicAPI/net9.0/PublicAPI.Unshipped.txt

@@ -2,4 +2,5 @@
 Microsoft.Identity.Web.BeforeTokenAcquisitionForApp
 Microsoft.Identity.Web.TokenAcquisitionExtensionOptions
 Microsoft.Identity.Web.TokenAcquisitionExtensionOptions.OnBeforeTokenAcquisitionForApp -> Microsoft.Identity.Web.BeforeTokenAcquisitionForApp?
+Microsoft.Identity.Web.TokenAcquisitionExtensionOptions.OnBeforeTokenAcquisitionForTestUser -> Microsoft.Identity.Web.BeforeTokenAcquisitionForTestUser?
 Microsoft.Identity.Web.TokenAcquisitionExtensionOptions.TokenAcquisitionExtensionOptions() -> void