Add workaround for long keys= in mqtt-publisher #10713

Job	Run time
rip-and-test	19m 18s
rip-and-test-clang	19m 36s
htmldocs	28m 52s
package-arch (debian:buster)	21m 54s
package-indep (debian:buster)	48m 46s
package-arch (debian:bullseye)	22m 48s
package-indep (debian:bullseye)	49m 4s
package-arch (debian:bookworm)	23m 56s
package-indep (debian:bookworm)	43m 12s
package-arch (debian:sid)	24m 17s
package-indep (debian:sid)	45m 22s
	5h 47m 5s

Provide feedback