Fix render_in returning non-html_safe string when render? is false

[Copilot]

When render? returns false, render_in returned a plain "" instead of "".html_safe, making it inconsistent with the happy path and causing TypeError when concatenating with other SafeBuffer strings.

Changes

• lib/view_component/base.rb: Return "".html_safe instead of "" in the render? false branch
• test/sandbox/test/rendering_test.rb: Add assertion that render_in output is html-safe when render? is false

# Before fix — raises TypeError when concatenated with SafeBuffer
render(MyComponent.new) + some_helper_returning_html  # => TypeError

# After fix
render(MyComponent.new).html_safe?  # => true

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[joelhawksley]

Looks good, please add a changelog

[joelhawksley]

@copilot please add a changelog entry

[Copilot]

@copilot please add a changelog entry

Added a changelog entry in docs/CHANGELOG.md under the ## main heading in commit 8733dad.