Bump alpine from 3.19.7 to 3.21.3 in /src/test/resources/org/jvnet/hudson/plugins/platformlabeler/alpine/3.19.7

Bump alpine from 3.19.7 to 3.21.3 in /src/test/resources/org/jvnet/hudson/plugins/platformlabeler/alpine/3.19.7 #1355