cargo-deny: Ignore private crates (#2814)

There's no point in having to specify the license value on all our unpublished
crates. This commit relaxes the license check for private crates.

Author: olix0r

deny.toml

@@ -26,6 +26,8 @@ deny = []
 copyleft = "deny"
 allow-osi-fsf-free = "neither"
 default = "deny"
+# Ignore local workspace license values for unpublished crates.
+private = { ignore = true }
 confidence-threshold = 0.8
 exceptions = [
     { allow = [