test: disable Debian ecosystem tests (#2520)

snapshot.debian.org has an expired certificate that is causing
intermittent failures depending on which IPv4 address is used.

https://bugs.debian.org/1079320

osv/ecosystems/debian_test.py

@@ -21,6 +21,8 @@
 from .. import ecosystems
 
 
+@unittest.skip(
+    "snapshot.debian.org certificate expiry: https://bugs.debian.org/1079320")
 class DebianEcosystemTest(unittest.TestCase):
   """Debian ecosystem helper tests."""