Postico2 private key field not entirely clickable (add/edit connections)

https://user-images.githubusercontent.com/998682/155327590-7f523a0f-2cca-4b15-acb9-37d5648f9140.mov

## What did you do?
- New Server -> connect via SSH tunnel
- I clicked on the Private Key field and nothing happened. Then I inspected more closely and it would seem, that there is an invisible tiny label on top of it, that is selectable and captures the click

## What did you expect to happen?

- I expected to see the entire field as button, to click it intuitively

## What software versions are you using?

Postico version:
Version 2.0beta (9346)

macOS version:
12.0.1, macOS Monterey, M1 Pro

Reproduce the New Server → connect via SSH tunnel flow on macOS and inspect the Private Key field shown in the issue video. The work is done when clicking anywhere in the field opens the private-key picker rather than being blocked by the invisible label.

Written by the indexing model from the issue text.