Bump mockgen to v1.5.0

[CecileRobertMichon]

Change the value of mockgen version here: https://github.com/kubernetes-sigs/cluster-api-provider-azure/blob/master/Makefile#L75

See golang/mock#405 (comment)

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In response to this:

Change the value of mockgen version here: https://github.com/kubernetes-sigs/cluster-api-provider-azure/blob/master/Makefile#L75

See golang/mock#405 (comment)

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[Evalle]

/assign