Install macOS from installer url fails on Mojave

[Dave Lebbing]

build 30108

When running a workflow on Mojave recovery partition that is set to install macOS from an installer url, the workflow quickly shows an error message stating:

DMG Failed to download via RAMDisk.

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I confirmed that the url for the installer could be accessed from another machine when this error occurred.

[Dave Lebbing]

Still had this issue after changing the installer file extension from sparseimage to dmg. Using 10.14.6 for both installer file and recovery environment.