Thanks Pavel for posting the patches for Rails 6 update.

I've applied this patch on the current trunk and a test fails:
<pre>
Failure:
AttachmentsTest#test_upload_and_resubmit_after_validation_failure [/builds/redmine-org/redmine/test/integration/attachments_test.rb:113]:
Expected at least 1 element matching "input[name="attachments[p0][description]"][value="My uploaded file"]", found 0..
Expected 0 to be >= 1.
bin/rails test test/integration/attachments_test.rb:99
</pre>

You can see the test results "here":https://gitlab.com/redmine-org/redmine/pipelines/113514724.
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sry, thanks for catching this, I was confused about the comment. Closing
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Let's keep it open, maybe we can fix the issue.
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This change passes all the tests now: https://gitlab.com/redmine-org/redmine/-/pipelines/280930686

The fail reported by me above was caused by another issue that was fixing as part of Rails 6.1 update.
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Committed the patch. Thank you.
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relates,Closed,29914,Migrate to Rails 6.1 with Zeitwerk autoloading