Updates serverless_neg_https_lb module version

Changes

• Updates serverless_neg_https_lb module version to v9.3.0 which is the first one allowing Terraform google provider version higher than v5:
  https://github.com/terraform-google-modules/terraform-google-lb-http/blob/f8ce32e245a89658ea1cba1ca5b3363ab2ded7af/versions.tf