Add Linux Mint to getdeps Debian package manager options

Summary:
X-link: facebookincubator/zstrong#909

Linux Mint is based on Ubuntu and installs correctly with the same options. This adds it to the supported versions so that running `sudo ./install-system-packages.sh` succeeds.

X-link: facebook/watchman#1234

Reviewed By: chadaustin

Differential Revision: D59666084

Pulled By: genevievehelsel

fbshipit-source-id: cfdee239be6358d4c8e2f1154391159a40ef91f4

build/fbcode_builder/getdeps/platform.py

@@ -272,7 +272,7 @@ def get_package_manager(self):
             return "homebrew"
         if self.distro in ("fedora", "centos", "centos_stream", "rocky"):
             return "rpm"
-        if self.distro.startswith(("debian", "ubuntu", "pop!_os")):
+        if self.distro.startswith(("debian", "ubuntu", "pop!_os", "mint")):
             return "deb"
         return None