[2.x] Fix delete button visibility in search filters

[hogan-tech]

Description

This PR fixes a UI bug in the Variable List page where the "Delete" (remove filter) button for search filters was not fully visible. The issue was caused by legacy table cell (td) settings in the template, which became problematic after upgrading the Flask-AppBuilder package. The button was partially hidden, with only its right border visible, making it difficult for users to remove filters.

What was changed:

• Adjusted the table cell settings in variable_list.html to ensure the remove filter button is always fully visible and accessible in the Variable List filter UI.

Related Issues

closes: #50296

Related PRs

• Airflow: Add 'Show record' option for variables
• Flask-AppBuilder: fix: filter list UI spacing between elements
• [2.x] Fix pools list page's delete button visibility in search filters

How to reproduce

1. Go to Admin → Variables in the Airflow UI.
2. Click "Add Filter" and select a filter.
3. Observe that the delete (remove filter) button is not fully visible (only the right border shows).

What you think should happen instead

The delete search filter button should be fully visible and easily clickable.

Additional context

• This issue appeared after upgrading Flask-AppBuilder, which changed some default table rendering behaviors.
• The fix is backward-compatible and only affects the Variable List page.

Screenshots

Before:

After:

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Please review and let me know if further adjustments are needed.

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[boring-cyborg]

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[pierrejeambrun]

Can you also fix it for the Pools template, that's exactly the same issue. pool_list.html

[hogan-tech]

Can you also fix it for the Pools template, that's exactly the same issue. pool_list.html

Thank you for reviewing. I've created a new PR to fix the same issue in the Pools list page:

[2.x] Fix pools list page's delete button visibility in search filters (#51161)

Please let me know if any further changes are needed.

[boring-cyborg]

Awesome work, congrats on your first merged pull request! You are invited to check our Issue Tracker for additional contributions.