Update micrometer-bom to 1.15.12

Closes gh-19302

Author: jgrandja

gradle/libs.versions.toml

@@ -1,6 +1,6 @@
 [versions]
 com-squareup-okhttp3 = "3.14.9"
-io-micrometer = "1.15.11"
+io-micrometer = "1.15.12"
 io-rsocket = "1.1.5"
 io-spring-javaformat = "0.0.47"
 io-spring-nohttp = "0.0.11"