Handle test failure of mock object

Fixup 4c26a38

https://rubyci.s3.amazonaws.com/amazon2/ruby-master/log/20250601T213003Z.fail.html.gz

```
1)
An exception occurred during: Mock.verify_count
File.birthtime accepts an object that has a #to_path method FAILED
Mock 'path' expected to receive to_path(:any_args) exactly 1 times
but received it 0 times
/home/chkbuild/chkbuild/tmp/build/20250601T213003Z/ruby/spec/ruby/core/file/birthtime_spec.rb:4:in 'block in <top (required)>'
/home/chkbuild/chkbuild/tmp/build/20250601T213003Z/ruby/spec/ruby/core/file/birthtime_spec.rb:3:in '<top (required)>'
```

Author: hsbt

spec/ruby/core/file/birthtime_spec.rb

@@ -18,6 +18,7 @@
     end
 
     it "accepts an object that has a #to_path method" do
+      File.birthtime(@file) # Avoid to failure of mock object with old Kernel and glibc
       File.birthtime(mock_to_path(@file))
     rescue NotImplementedError => e
       skip e.message if e.message.start_with?("birthtime() function")