Block runningboard access in the Network Process sandbox again on macOS and address Bug 259229 by always holding a background assertion on the network process (so that it never suspends).
Pull request: https://github.com/WebKit/WebKit/pull/15883
Committed 266101@main (2d0174d8fad3): <https://commits.webkit.org/266101@main> Reviewed commits have been landed. Closing PR #15883 and removing active labels.
<rdar://problem/112413309>