Jetpack Search Block: Incorrect Heading sequence for filters in Footer Widget

### Impacted plugin

Jetpack, Search

### Quick summary

When the Jetpack Search block is added to the footer widget area, the filter headings are generated as H4 without a preceding H3, which can negatively impact SEO due to improper heading hierarchy.

Issue reported by a user here: 8599734-zd-a8c

### Steps to reproduce

1. Go to Appearance > Customize > Widgets > Footer.
2. Add the Jetpack Search block to the Footer widget area.
3. Enable filters (Tags, Categories) within the Jetpack Search block


### A clear and concise description of what you expected to happen.

The filter headings should follow a sequential heading order, ideally starting with H3, or there should be an option to customize the heading level.

### What actually happened

The filter headings are automatically generated as H4, despite no H3 heading preceding them, which may cause SEO issues.

### Impact

Some (< 50%)

### Available workarounds?

No but the platform is still usable

### If the above answer is "Yes...", outline the workaround.

No direct workarounds within the block settings. A custom CSS workaround can be implemented, but it requires manual intervention and it doesn't solve the issue, as it can only eventually style the H4 to look like H3, but it's not what user really needs.

### Platform (Simple and/or Atomic)

_No response_

### Logs or notes

_No response_

Begin at the Jetpack Search block when it is rendered in the footer widget, with the Tags and Categories filters enabled. Compare its heading hierarchy with the expected sequential order, then verify the result in the Appearance > Customize > Widgets > Footer reproduction steps.

Written by the indexing model from the issue text.