Bump alpine from 3.19.6 to 3.21.1 in /src/test/resources/org/jvnet/hudson/plugins/platformlabeler/alpine/3.19.6

Bump alpine from 3.19.6 to 3.21.1 in /src/test/resources/org/jvnet/hudson/plugins/platformlabeler/alpine/3.19.6 #1343