Update banner content to promote the 26Q2 survey

[zanderso]

The survey will run from 6/1 9am PT to 6/12 EOD.

Presubmit checklist

• If you are unwilling, or unable, to sign the CLA, even for a tiny, one-word PR, please file an issue instead of a PR.
• If this PR is not meant to land until a future stable release, mark it as draft with an explanation.
• This PR follows the Google Developer Documentation Style Guidelines—for example, it doesn't use i.e. or e.g., and it avoids I and we (first-person pronouns).
• This PR uses semantic line breaks
  of 80 characters or fewer.

[gemini-code-assist]

Code Review

This pull request updates the site banner in site.yml to invite users to take the Q2 survey instead of announcing the Flutter 3.44 release. The review feedback suggests improving the HTML link by removing the first-person pronoun 'our' to comply with style guidelines and adding rel="noopener" to the anchor tag for security.

[gemini-code-assist]

According to the Google Developer Documentation Style Guidelines, first-person pronouns like 'our' should be avoided. Additionally, when using target='_blank', it is a security best practice to include rel='noopener' to prevent reverse tabnabbing. Consider updating the link text to 'Take the Q2 survey' and adding rel='noopener'.

  <a href="https://google.qualtrics.com/jfe/form/SV_3drKjSfjNeLZfq6?Source=Website" target="_blank" rel="noopener">Take the Q2 survey</a>.

[sfshaza2]

I do prefer "take the...survey" over "take OUR...survey". For me, it's part of the open source mentality.

[flutter-website-bot]

Staged preview of the updated docs.flutter.dev site (updated for commit 3c97796):

https://flutter-docs-prod--docs-pr13453-zanderso-patch-1-4zk8vde4.web.app

[parlough]

Thanks! Feel free to land when ready.

There might be a failed check due to formatter changes, feel free to ignore and merge past it. #13449 fixes it.

[sfshaza2]

I'm approving, but please do make these edits.

[sfshaza2]

lgtm, with minor fixes