Ensure delete works as expected in dataframe headers

[hannahblair]

Description

Ensures the backspace button works when editing the value of dataframe headers.

Also fixes an issue I found where if you clear the value of a dataframe header, you can still "find" and click on the textarea again and edit it.

Closes: #(issue)

AI Disclosure

We encourage the use of AI tooling in creating PRs, but the any non-trivial use of AI needs be disclosed. E.g. if you used Claude to write a first draft, you should mention that. Trivial tab-completion doesn't need to be disclosed. You should self-review all PRs, especially if they were generated with AI.

• I used AI to... [fill here]
• I did not use AI

🎯 PRs Should Target Issues

Before your create a PR, please check to see if there is an existing issue for this change. If not, please create an issue before you create this PR, unless the fix is very small.

Not adhering to this guideline will result in the PR being closed.

Testing and Formatting Your Code

1. PRs will only be merged if tests pass on CI. We recommend at least running the backend tests locally, please set up your Gradio environment locally and run the backed tests: bash scripts/run_backend_tests.sh

2. Please run these bash scripts to automatically format your code: bash scripts/format_backend.sh, and (if you made any changes to non-Python files) bash scripts/format_frontend.sh

[gradio-pr-bot]

🪼 branch checks and previews

•	Name	Status	URL
	Spaces	ready!	Spaces preview
	Storybook	ready!	Storybook preview
🦄	Changes	detected!	Details

---

Install Gradio from this PR

pip install https://gradio-pypi-previews.s3.amazonaws.com/66ec50be6739633c64adb33ac9773b9e9771f7f7/gradio-6.5.1-py3-none-any.whl

Install Gradio Python Client from this PR

pip install "gradio-client @ git+https://github.com/gradio-app/gradio@66ec50be6739633c64adb33ac9773b9e9771f7f7#subdirectory=client/python"

Install Gradio JS Client from this PR

npm install https://gradio-npm-previews.s3.amazonaws.com/66ec50be6739633c64adb33ac9773b9e9771f7f7/gradio-client-2.0.4.tgz

[gradio-pr-bot]

🦄 no changes detected

This Pull Request does not include changes to any packages.

__No changes detected. __

---

---

‼️ Changeset not approved. Ensure the version bump is appropriate for all packages before approving.

• Maintainers can approve the changeset by checking this checkbox.

Something isn't right?

• Maintainers can change the version label to modify the version bump.
• If the bot has failed to detect any changes, or if this pull request needs to update multiple packages to different versions or requires a more comprehensive changelog entry, maintainers can create the changelog file directly.