Issues are not included in search when is:pr is removed

[StefanieSenger]

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Bug

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Previously, when filtering issues and pull requests in a project, it was possible to remove the is:pr filter from the search field to see both issues and PRs.

Unfortunately however, this doesn't work anymore:

• If the search starts in the "Pull Requests" section, removing is:pr (as shown in this screenshot) does not display issues anymore. The results remain limited to PRs.
  
• The reverse still works: if the search starts in the "Issues" section, removing is:issue correctly includes PRs.

At scikit-learn, we rely on community contributors to easily search for related or possibly duplicated issues and PRs before opening new ones and this change in behavior makes it harder to do so.

It seems like a bug to me, rather than intentional?

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