Some of the failures are:

java.lang.IllegalArgumentException: Java 8 date/time type `java.time.Instant` not supported by default: add Module "com.fasterxml.jackson.datatype:jackson-datatype-jsr310" to enable handling

which indicates adding this dependency may help:

<dependency>
    <groupId>com.fasterxml.jackson.datatype</groupId>
    <artifactId>jackson-datatype-jsr310</artifactId>
    <version>${jackson.version}</version>
</dependency>

@PascalSchumacher when I pulled your PR and added the jar as noted above I got a clean build and test.
I am assuming the new jar is also added to the notice.txt file.

@dbmalkovsky Thanks, but the question is: Why is jackson-datatype-jsr310 required when using Jackson 2.12?

On further thinking I believe it is best to wait with the update until Spring Boot uses Jackson 2.12 too.

I guess this is the reason for the test failures: FasterXML/jackson-databind#2683