Fix NoMethodError in Gem.try_activate when activation conflicts occur

[hsbt]

What was the end-user or developer problem that led to this PR?

When find_unloaded_by_path returns nil, the subsequent spec.name call raises NoMethodError because spec has been overwritten. Save the gem name before reassigning spec.

Fixes https://bugs.ruby-lang.org/issues/21954

Make sure the following tasks are checked

• Describe the problem / feature
• Write tests for features and bug fixes
• Write code to solve the problem
• Make sure you follow the current code style and write meaningful commit messages without tags

[Copilot]

Pull request overview

Fixes a NoMethodError in Gem.try_activate when an activation conflict occurs and find_unloaded_by_path returns nil, by preserving the originally selected spec’s name before reassigning spec.

Changes:

• Preserve spec.name before reassigning spec inside the Gem.try_activate conflict-handling rescue path.
• Add a regression test covering the activation-conflict scenario that previously triggered the NoMethodError.

Reviewed changes

Copilot reviewed 2 out of 2 changed files in this pull request and generated no comments.

File	Description
lib/rubygems.rb	Prevents NoMethodError by avoiding dereferencing spec after it may have been set to nil during conflict recovery.
test/rubygems/test_gem.rb	Adds a regression test ensuring Gem.try_activate does not raise when an older version is activated and a newer-only file is requested.

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[hsbt]

@Edouard-chin Could you look this?

[jeremyevans]

I've tested this and it fixed the Redmine issue.

[hsbt]

@jeremyevans Thanks!

[Edouard-chin]

🤦 Thanks for the fix !

[hsbt]

@jeremyevans I missed to backport this to 4.0.9 release. I will do that for 4.0.10 at 8th, April. Sorry to your inconvenience.