openthread_border_router: bump OTBR to release-v2026.09.0 once published (needed to test ePSKc / python-otbr-api#267)

[lboue]

Description

Description

Once the openthread/ot-br-posix release-v2026.09.0 tag is published,
could the openthread_border_router add-on be bumped to that revision
(stable and/or beta)?

Motivation

release-v2026.09.0 is expected to include the ePSKc (ephemeral key /
Thread 1.4 Credentials Sharing) REST endpoints added in
openthread/ot-br-posix#3480 (/node/ba-epskc/state and
/node/ba-epskc/key).

These endpoints are required to test the client-side implementation
currently proposed in home-assistant-libs/python-otbr-api#267:
home-assistant-libs/python-otbr-api#267

Without a build of the add-on that includes this OTBR revision, it's
not possible to validate the wire contract end-to-end against a
"real" Home Assistant setup (only against a manually-built otbr-agent,
as the python-otbr-api PR author already did).

Additional context

• Roadmap oppornity: Investigate the current state of Thread credential sharing to deduct potential improvements OpenHomeFoundation/roadmap#137
• Related python-otbr-api PR: Add client support for ephemeral key (ePSKc) credentials sharing home-assistant-libs/python-otbr-api#267
• Underlying ot-br-posix REST endpoints: [rest] add endpoints for Border Agent ephemeral key (ePSKc) openthread/ot-br-posix#3480
• Related draft Core PR: Add Thread credential sharing to OTBR core#177371
• Related draft frontend PR: Add Thread credential sharing to the Thread panel frontend#53330
• Reference for how OTBR bumps are typically done: openthread_border_router: Bump stable to v2026.07.0 & beta to v2026.08.0 #4763

[github-actions]

Hi @lboue, thank you for your contribution!

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