Bump io.github.problem4j:problem4j-core from 1.3.0 to 1.3.1 (#57)

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gradle/libs.versions.toml

@@ -1,6 +1,6 @@
 [versions]
 nmcp = "1.4.3"
-problem4j-core = "1.3.0"
+problem4j-core = "1.3.1"
 problem4j-jackson2 = "1.3.0"
 spotless = "8.1.0"
 spring-boot = "3.5.9"