Bump alpine from 3.18.11 to 3.21.2 in /src/test/resources/org/jvnet/hudson/plugins/platformlabeler/alpine/3.18.11

Bump alpine from 3.18.11 to 3.21.2 in /src/test/resources/org/jvnet/hudson/plugins/platformlabeler/alpine/3.18.11 #1342