fix(MatrixRTCSession): replace no-arg .finally() with .then(fn, fn) to fix crash on React Native / Hermes

[JeanLuX]

Fixes #5308

What

ensureRecalculateSessionMembers() called .finally() with no argument to swallow a previous rejection before chaining the next recalculation.

On React Native / Hermes, the RN Promise polyfill (promise/setimmediate/finally.js) requires onFinally to be a callable — passing undefined throws immediately:

TypeError: undefined is not a function

This rejects initialMembershipCalculated for every room at startup, silently breaking the entire RTC session membership layer on all React Native clients.

Fix

Replace .finally().then(fn) with .then(fn, fn) — semantically equivalent on all runtimes:

-    this.recalculateSessionMembersPromise = this.recalculateSessionMembersPromise.finally().then(() => this.recalculateSessionMembers());
+    this.recalculateSessionMembersPromise = this.recalculateSessionMembersPromise.then(
+      () => this.recalculateSessionMembers(),
+      () => this.recalculateSessionMembers(),
+    );

File: src/matrixrtc/MatrixRTCSession.ts — ensureRecalculateSessionMembers()

Verified on

Component	Version
matrix-js-sdk	41.4.0
React Native	0.83.6
Hermes	bundled with RN 0.83.6
Expo SDK	55

Checklist

• Semantics preserved — recalculation runs on both resolve and reject
• No behaviour change on browser / Node.js runtimes
• Unit tests pass locally (yarn test)
• Signed-off-by / CLA (if required)