Accordion header IDs collide when the same view display is rendered twice

Problem/Motivation

When the same Views Bootstrap Accordion display is rendered more than once on a page with different arguments (for example two embeddings of the same view with different contextual filters), the markup produces duplicate id attributes. Duplicate IDs are an accessibility issue: they break the unique-ID requirement in HTML and can confuse assistive technologies.

Collapse panel IDs already use the unique instance prefix from ViewsBootstrap::getUniqueId() / Html::getUniqueId():

{{ id }}-collapse-{{ clean_key }}

Header IDs do not. They are built only from the group key:

heading{{ clean_key }}

With identical group values (e.g. years 2026, 2025, 2024), both accordions emit the same header IDs (headingkey--2026, etc.). aria-labelledby on the second accordion’s panels then points at the first accordion’s headers, so assistive tech can announce the wrong label.

Steps to reproduce

1. Create a view using the Bootstrap Accordion style, with grouping that produces stable keys (e.g. year).
2. Place that view display twice on the same page with different arguments (e.g. two embeddings of the same display with different contextual filter values).
3. Inspect the markup.
4. Observe duplicated header IDs such as headingkey--2026, and aria-labelledby on the second accordion resolving to headers from the first.

Proposed resolution

Prefix accordion header IDs with the same unique {{ id }} already used for collapse panels, and keep aria-labelledby in sync:

{% set heading_id = id ~ '-heading-' ~ clean_key %}

Use id="{{ heading_id }}" on the header and aria-labelledby="{{ heading_id }}" on the panel. data-bs-target / data-bs-parent are already unique and do not need changes.

Remaining tasks

• Review the patch / merge request
• Commit and tag a new release once the fix is merged

User interface changes

None.

API changes

None.

Data model changes

None.