ActionMailer Email Preview - show date header when present

[sampatbadhe]

Detail

ActionMailer Email Preview - show date header when present or fallback to Time.current.rfc2822

Resolves #49788

Co-authored-by: @allisonphillips

Checklist

Before submitting the PR make sure the following are checked:

• This Pull Request is related to one change. Changes that are unrelated should be opened in separate PRs.
• Commit message has a detailed description of what changed and why. If this PR fixes a related issue include it in the commit message. Ex: [Fix #issue-number]
• Tests are added or updated if you fix a bug or add a feature.
• CHANGELOG files are updated for the changed libraries if there is a behavior change or additional feature. Minor bug fixes and documentation changes should not be included.

[Edouard-chin]

Should be quick and easy to add a test, mind adding one similar to this one ?

rails/railties/test/application/mailer_previews_test.rb

Line 962 in 2b09327

test "mailer preview sender tags" do

[sampatbadhe]

Thank you for review @Edouard-chin. I have added tests, could you please check.

[Edouard-chin]

A minor suggestion, but it looks great otherwise. Thanks!

[jonathanhefner]

I felt like this was worth a CHANGELOG entry, so I pushed a commit to add one.

Thank you, @sampatbadhe! 📫 And thank you, @Edouard-chin! 👋