Do not use SIGTERM

[tmat]

Workaround for #49307

Proper fix requires change in runtime: dotnet/runtime#116556

[Copilot]

Pull Request Overview

This PR implements a workaround for #49307 by no longer using SIGTERM on Linux, updating tests and the process runner accordingly.

• Unskip tests previously blocked by SIGTERM issues and adjust assertions to only validate SIGKILL behavior.
• Comment out OS-specific branches in tests and update expected output messages.
• Change ProcessRunner to always use SIGKILL instead of conditional SIGTERM/SIGKILL.

Reviewed Changes

Copilot reviewed 2 out of 2 changed files in this pull request and generated 2 comments.

File	Description
test/dotnet-watch.Tests/HotReload/ApplyDeltaTests.cs	Removed skips, commented out Windows/Linux branches, updated messages
src/BuiltInTools/dotnet-watch/Internal/ProcessRunner.cs	Always invoke sys_kill with SIGKILL, removed SIGTERM usage

Comments suppressed due to low confidence (2)

test/dotnet-watch.Tests/HotReload/ApplyDeltaTests.cs:813

• Commenting out the Linux branch removes coverage for Unix termination behavior. Instead of deleting the branch, use runtime conditionals or platform-specific skips so both code paths remain tested.

// SIGTERM no longer works on Linux https://github.com/dotnet/sdk/issues/49307

test/dotnet-watch.Tests/HotReload/ApplyDeltaTests.cs:423

• The test was unskipped despite the underlying SDK issue still open. This may cause test failures on CI. Ensure the root cause is resolved or mark the test as platform-specific skip until fixed upstream.

[Theory]

[tmat]

Superseded by #49336