fix: disable save button upon submitting #17181

Job	Run time
Core Basic (18.x)	7m 27s
Core Basic (20.x)	6m 48s
Core Basic - Plone 5 (18.x)	7m 17s
Core Blocks (18.x)	7m 33s
Core Blocks (20.x)	7m 29s
Core Blocks - Listing (18.x)	6m 31s
Core Blocks - Listing (20.x)	6m 18s
Core Content (18.x)	3m 38s
Core Content (20.x)	3m 58s
Core Control Panels (18.x)	4m 21s
Coresandbox (18.x)	4m 21s
Core Control Panels (20.x)	4m 11s
Core Volto Slate (18.x)	7m 50s
Project Generator (18.x)	5m 36s
Guillotina (18.x)	1m 16s
Core Volto Slate (20.x)	7m 27s
Multilingual (18.x)	3m 55s
Project Generator (20.x)	5m 41s
Multilingual in Seamless Mode (18.x)	2m 1s
Seamless Mode (18.x)	1m 14s
Working Copy (18.x)	3m 37s
	1h 48m 29s

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