Cast int to string in the I9813_QuickSubmitSubmissionProgressType upgrade script that fixes wrong values for submission_progress inserted by the QuickSubmit plugin

[bozana]

s. https://forum.pkp.sfu.ca/t/error-during-upgrade-ojs-3-4-0-5-to-3-4-0-6-invalid-datetime-format-1292-truncated-incorrect-double-value-files/89623

PRs:
stable-3_4_0: pkp/ojs#4376
main: pkp/ojs#4381