Electron 43.7.0 threw 'Invalid guestInstanceId' from <webview>'s
disconnectedCallback for a loaded guest (electron/electron#53989), so a
webview React removed and re-inserted kept a dead guest id: the tab went
blank, reload did nothing, and the destroyed listener never fired.
43.7.4 (electron/electron#54097) returns early when the guest is gone.
Raises the runtime floor test to 43.7.4 so a downgrade cannot re-ship it.
Fixes STA-8757