Health check errors silently dropped when channel buffer full

**Component:** pkg/plugin/plugin.go:153-156, pkg/plugin/plugin_v2.go:156-158 **Affected Version:** aws-encryption-provider @ 4341c70 (all versions) **Found by:** Source audit **TLP:** TLP:Amber

// pkg/plugin/plugin.go:152-156 (also plugin_v2.go:155-159)
if err != nil {
    select {
    case p.healthCheck.healthCheckErrc <- err:
    default:
        // ERROR SILENTLY DROPPED
    }