Adapt deny.toml to use git-fetch-with-cli.

It uses its own escape hatch to force use of the CLI, much in the same way
that Cargo does.

This is critical for Windows.

Ref: EmbarkStudios/cargo-deny#420

deny.toml

@@ -16,6 +16,13 @@ yanked = "warn"
 # 2019-12-17 there are no security notice advisories in
 # https://github.com/rustsec/advisory-db
 notice = "warn"
+
+# If this is true, then cargo deny will use the git executable to fetch advisory database.
+# If this is false, then it uses a built-in git library.
+# Setting this to true can be helpful if you have special authentication requirements that cargo-deny does not support.
+# See Git Authentication for more information about setting up git authentication.
+git-fetch-with-cli = true
+
 # A list of advisory IDs to ignore. Note that ignored advisories will still
 # output a note when they are encountered.