Fix main build break: remove redundant DisplayName=nameof in dotnet.Tests (MSTEST0071)

[Evangelink]

Problem

main is currently failing to build (dotnet.Tests.csproj) with 48 error MSTEST0071:

test/dotnet.Tests/CommandTests/New/DotnetAddPostActionTests.cs(37,10): error MSTEST0071:
  The 'DisplayName' is the same as the test method name 'AddRefFindsOneDefaultProjFileInOutputDirectory' and can be removed

Root cause

The testfx dependency bump (#54765) merged after the dotnet.Tests MSTest migration (#54905). Under MSTestAnalysisMode=Recommended (set in test/Directory.Build.props), the analyzer now promotes MSTEST0071 to an error. The migrated New post-action tests use [TestMethod(DisplayName = nameof(MethodName))], where the display name is identical to the method name — exactly what MSTEST0071 flags as redundant.

This breaks the build for every PR that merges with current main (e.g. observed while investigating #54904).

Fix

Drop the redundant DisplayName = nameof(...) from the 24 affected [TestMethod] attributes across:

• test/dotnet.Tests/CommandTests/New/DotnetAddPostActionTests.cs
• test/dotnet.Tests/CommandTests/New/DotnetRestorePostActionTests.cs
• test/dotnet.Tests/CommandTests/New/DotnetSlnPostActionTests.cs

The display name now defaults to the method name — identical observable behavior, no test renames.

Scope notes

• Only dotnet.Tests (an MSTest.Sdk project) is affected. The TemplateEngine unit-test projects also use DisplayName = nameof, but they are still xUnit (Microsoft.NET.Sdk), so MSTEST0071 does not apply and they are intentionally left untouched.
• This is split out from Migrate dotnet-new.IntegrationTests to MSTest.Sdk on MTP #54904 (which only fixes a separate CS0104 in dotnet-new.IntegrationTests) per the same incremental-migration approach.

Co-authored-by: Copilot 223556219+Copilot@users.noreply.github.com

[Copilot]

Pull request overview

Fixes a dotnet.Tests build break on main caused by MSTest analyzers promoting MSTEST0071 (redundant DisplayName matching the method name) to an error under MSTestAnalysisMode=Recommended.

Changes:

• Removes redundant [TestMethod(DisplayName = nameof(...))] usage where the display name equals the test method name.
• Replaces those attributes with plain [TestMethod] across the affected dotnet new post-action test files.

Show a summary per file

File	Description
test/dotnet.Tests/CommandTests/New/DotnetAddPostActionTests.cs	Drops redundant DisplayName = nameof(...) from [TestMethod] attributes to satisfy MSTEST0071.
test/dotnet.Tests/CommandTests/New/DotnetRestorePostActionTests.cs	Same: removes redundant DisplayName from [TestMethod].
test/dotnet.Tests/CommandTests/New/DotnetSlnPostActionTests.cs	Same: removes redundant DisplayName from [TestMethod] (including solution-related post-action tests).

Copilot's findings

• Files reviewed: 3/3 changed files
• Comments generated: 0

[Evangelink]

/ba-g test failures are unrelated to this PR. Merging to unblock main.