Attempt to fix flaky test by adding host.mac to all the fake_hosts do…

…cuments (#178648)

Fixes #178578

The hypothesis is that during adding context variables, it uses a
document that does not have `host.mac`, and in some of the `fake_host`
documents we have this condition, so I fixed that.

x-pack/packages/kbn-data-forge/src/data_sources/fake_hosts/index.ts

@@ -91,6 +91,7 @@ export const generateEvent: GeneratorFunction = (config, schedule, index, timest
       '@timestamp': timestamp.toISOString(),
       host: {
         name: `host-${index}`,
+        mac: ['00-00-5E-00-53-23', '00-00-5E-00-53-24'],
         network: {
           name: `network-${index}`,
           ingress: {
@@ -134,6 +135,7 @@ export const generateEvent: GeneratorFunction = (config, schedule, index, timest
       '@timestamp': timestamp.toISOString(),
       host: {
         name: `host-${index}`,
+        mac: ['00-00-5E-00-53-23', '00-00-5E-00-53-24'],
         network: {
           name: `network-${index}`,
         },