fix(readme): update broken Slack link

[Axel-DaMage]

What: Closes #12546, replaced https://slack.patternfly.org with https://patternfly.slack.com
in the README, matching the fix applied in patternfly-org#3364.

Additional issues: patternfly-org#3364 (previous fix in the docs site)

Summary by CodeRabbit

• Documentation
  • Updated the Community Slack link in the README to the new workspace URL.

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[coderabbitai]

Walkthrough

Updates the README Slack link and adds explicit aria-haspopup="listbox" handling to MenuToggle plus its Select-based example usages.

Changes

README Link Update

Layer / File(s)	Summary
Update Slack URL in README README.md	Changes the Community section Slack link from the old URL to https://patternfly.slack.com.

MenuToggle listbox semantics

Layer / File(s)	Summary
Add aria-haspopup support packages/react-core/src/components/MenuToggle/MenuToggle.tsx	Extends MenuToggleProps with aria-haspopup, sets a default value, and forwards it to rendered buttons in the typeahead, split-button, and default paths.
Set listbox popup on Select toggles packages/react-core/src/components/Form/examples/FormState.tsx, packages/react-core/src/components/LoginPage/examples/LoginPageLanguageSelect.tsx, packages/react-core/src/components/Select/examples/*, packages/react-core/src/components/Toolbar/examples/*, packages/react-core/src/components/Tooltip/examples/TooltipOptions.tsx	Updates Select-based toggle renderers to pass aria-haspopup="listbox" on the underlying MenuToggle elements.

Estimated code review effort: 2 (Simple) | ~10 minutes

Suggested reviewers: nicolethoen, thatblindgeye

🚥 Pre-merge checks | ✅ 4 | ❌ 1

❌ Failed checks (1 warning)

Check name	Status	Explanation	Resolution
Out of Scope Changes check	⚠️ Warning	The PR also adds aria-haspopup and MenuToggle API changes across many Select/Toolbar examples, which are unrelated to the README fix.	Remove the accessibility/MenuToggle changes or split them into a separate PR focused on that behavior.

✅ Passed checks (4 passed)

Check name	Status	Explanation
Linked Issues check	✅ Passed	The README link is updated from the broken Slack URL to patternfly.slack.com, satisfying the linked issue.
Docstring Coverage	✅ Passed	No functions found in the changed files to evaluate docstring coverage. Skipping docstring coverage check.
Description Check	✅ Passed	Check skipped - CodeRabbit’s high-level summary is enabled.
Title check	✅ Passed	The title clearly matches the main change: fixing the README’s broken Slack link.

✨ Finishing Touches

🧪 Generate unit tests (beta)

• Create PR with unit tests

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[Axel-DaMage]

Hi! I accidentally pushed a commit meant for a different issue into this branch, I have force-pushed to remove it, so this PR is now back to just the README link fix.
Please ignore the outdated modified CodeRabbit summary above.