feat(3p/gerrit): Upgrade Gerrit and plugins to v3.4.0

Brings us back to a stable version of Gerrit instead of a random
commit. Note that Gerrit 3.4.1 is out, but due to a bug it can not be
built publicly because it accidentally points at a private
submodule (this is being fixed upstream).

Change-Id: I0376c63a649498cef999dfa99bfccba511f2c8da
Reviewed-on: https://cl.tvl.fyi/c/depot/+/3444
Tested-by: BuildkiteCI
Reviewed-by: lukegb <lukegb@tvl.fyi>

third_party/gerrit/0006-Always-use-Google-Fonts.patch

@@ -1,4 +1,4 @@
-From e5c8621646bbde242453a1ac6b0b82f6279789e0 Mon Sep 17 00:00:00 2001
+From d71f51afe12a280b92831070a583b15c8b6bc2f4 Mon Sep 17 00:00:00 2001
 From: Luke Granger-Brown <git@lukegb.com>
 Date: Sat, 11 Jul 2020 00:46:13 +0000
 Subject: [PATCH 6/7] Always use Google Fonts.
@@ -24,5 +24,5 @@ index a9cfceb3b6..9c287c6e45 100644
      }
  
 -- 
-2.29.2
+2.32.0