Upgrade stable Rust to 1.50 version

[evdokimovs]

Synopsis

Rust v1.50 was released, so we need to upgrade it.

Checklist

• Created PR:
  • [x] In draft mode
  • [x] Name contains Draft: prefix
  • [x] Name contains issue reference
  • [x] Has k:: labels applied
  • [x] Has assignee
• [x] Documentation is updated (if required)
• [x] Tests are updated (if required)
• [x] Changes conform code style
• [x] CHANGELOG entry is added (if required)
• [x] FCM (final commit message) is posted
  • [x] and approved
• [x] Review is completed and changes are approved
• Before merge:
  • [x] Milestone is set
  • [x] PR's name and description are correct and up-to-date
  • [x] Draft: prefix is removed
  • [x] All temporary labels are removed

[evdokimovs]

FCM

Upgrade stable Rust to 1.50 version

- update Cargo deps
- upgrade 'actix-cors' crate to 0.5 version

Additionally:
- upgrade Firefox to 85.0.2 version for E2E tests