Ensure empty plugin settings are saved correctly (#22891) #7330

Job	Run time
Client	1m 33s
Javascript	3m 25s
UI (0)	17m 10s
PHP (UnitTests, 7.2, Mysql, PDO_MYSQL)	1s
UI (1)	17m 2s
PHP (UnitTests, 8.2, Mariadb, PDO_MYSQL)	1s
UI (2)	14m 10s
PHP (UnitTests, 8.4, Mysql, MYSQLI)	1s
UI (3)	12m 54s
PHP (SystemTestsPlugins, 7.2, Mysql, PDO_MYSQL)	4m 8s
PHP (SystemTestsPlugins, 8.2, Mariadb, PDO_MYSQL)	4m 7s
PHP (SystemTestsPlugins, 8.4, Mysql, MYSQLI)	2m 25s
PHP (SystemTestsCore, 7.2, Mysql, PDO_MYSQL)	5m 41s
PHP (SystemTestsCore, 8.2, Mariadb, PDO_MYSQL)	7m 13s
PHP (SystemTestsCore, 8.4, Mysql, MYSQLI)	4m 25s
PHP (IntegrationTestsCore, 7.2, Mysql, PDO_MYSQL)	12m 30s
PHP (IntegrationTestsCore, 8.2, Mariadb, PDO_MYSQL)	10m 54s
PHP (IntegrationTestsCore, 8.4, Mysql, MYSQLI)	9m 7s
PHP (IntegrationTestsPlugins, 7.2, Mysql, PDO_MYSQL)	8m 3s
PHP (IntegrationTestsPlugins, 8.2, Mariadb, PDO_MYSQL)	8m 2s
PHP (IntegrationTestsPlugins, 8.4, Mysql, MYSQLI)	9m 6s
	2h 31m 58s

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