Update slf4j monorepo to v2.0.15

[renovate]

This PR contains the following updates:

Package	Change	Age	Adoption	Passing	Confidence
org.slf4j:slf4j-simple (source, changelog)	2.0.14 -> 2.0.15
org.slf4j:slf4j-api (source, changelog)	2.0.14 -> 2.0.15
org.slf4j:jcl-over-slf4j (source, changelog)	2.0.14 -> 2.0.15

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[coveralls]

coverage: 80.54%. remained the same
when pulling 4567658 on renovate/slf4j-monorepo
into a053c56 on master.