Fix/firefox release

[kbuffardi]

Bump version to fix error:

Run npm run sign:firefox:unlisted

> browser.cpp@0.3 sign:firefox:unlisted
> node scripts/sign-firefox-unlisted.mjs

Building web extension from /home/runner/work/browser.cpp/browser.cpp/dist-firefox
Waiting for validation...

WebExtError: Submission failed (2): Conflict
{
  "version": [
    "Version 0.3 already exists."
  ]
}
    at file:///home/runner/.npm/_npx/43d181ce0e38748d/node_modules/web-ext/lib/cmd/sign.js:101:13
    at process.processTicksAndRejections (node:internal/process/task_queues:103:5)
    at async Program.execute (file:///home/runner/.npm/_npx/43d181ce0e38748d/node_modules/web-ext/lib/program.js:270:7)
    at async file:///home/runner/.npm/_npx/43d181ce0e38748d/node_modules/web-ext/bin/web-ext.js:13:1

/home/runner/work/browser.cpp/browser.cpp/scripts/firefox-webext.js:49
    throw new Error(`web-ext exited with status ${result.status ?? 'unknown'}.`);
          ^