Update dependency io.micronaut:micronaut-core-bom to v5.1.8 (#2058)

Co-authored-by: renovate[bot] <29139614+renovate[bot]@users.noreply.github.com>

Author: renovate[bot]

gradle/libs.versions.toml

@@ -1,7 +1,7 @@
 [versions]
 
 # Micronaut
-micronaut = "5.1.7"
+micronaut = "5.1.8"
 micronaut-gradle-plugin = "5.0.2"
 micronaut-test-resources = "4.0.0"