Make dependency to maven-core explicit in tycho-sbom plugin

This dependency is indirectly contributed by CycloneDX 2.8.0, but not by
2.8.1. Given that it is required for compilation and to avoid errors
when updating this library, is it now added as an explicit dependency.

See #4085

tycho-sbom/pom.xml

@@ -25,6 +25,11 @@
 			<artifactId>maven-plugin-api</artifactId>
 		</dependency>
 
+		<dependency>
+			<groupId>org.apache.maven</groupId>
+			<artifactId>maven-core</artifactId>
+		</dependency>
+
 		<dependency>
 			<groupId>org.cyclonedx</groupId>
 			<artifactId>cyclonedx-maven-plugin</artifactId>