fix: reconnect to DB after long backup upload in Google Drive integra…

[kaulith]

Closes #17

Problem

upload_system_backup_to_google_drive() runs mysqldump as a subprocess and uploads large files to Google Drive. Both operations take significant time with zero DB activity.

MySQL's wait_timeout kills the idle connection.

When the function reaches
frappe.db.set_single_value("Google Drive", "last_backup_on", ...),
the write fails on the dead connection.

This causes last_backup_on to never update even though backups reach Google Drive successfully.

Fix

Wrap the set_single_value call in a try/except that reconnects on failure:

try:
    frappe.db.set_single_value("Google Drive", "last_backup_on", frappe.utils.now_datetime())
except Exception:
    frappe.db.connect()
    frappe.db.set_single_value("Google Drive", "last_backup_on", frappe.utils.now_datetime())

Testing

Tested with a 4.4 GB database backup file.

Without the fix, the RQ job fails with InterfaceError(0, '').

With the fix, last_backup_on updates correctly after a 51-minute job (well beyond MySQL's 600s/1500 wait_timeout).