Upgrade JGit to 5.9.0.202009080501-r

Align with the latest JGit actual release version used in core Gerrit
master branch. That is, before it started using non-released JGit
versions based on commits.

The latter are contained by one or a few recent tags in JGit, but those
tags are only release candidates. Hence they have no maven artifact or
published sha1 for them yet. Once their corresponding formal release is
ready (JGit 5.10.0 here), this used jgit version may be amended further.

Change-Id: I44826e38f4957c8e68be24d8ecc5f2df90e3bdf9

external_plugin_deps.bzl

diff --git a/external_plugin_deps.bzl b/external_plugin_deps.bzl
index b2231a0..d200f60 100644
--- a/external_plugin_deps.bzl
+++ b/external_plugin_deps.bzl
@@ -100,8 +100,8 @@
     maven_jar(
         name = "jgit",
         artifact =
-            "org.eclipse.jgit:org.eclipse.jgit:5.8.1.202007141445-r",
-        sha1 = "3b200e97843918969d0375a6e2184990b8e731e9",
+            "org.eclipse.jgit:org.eclipse.jgit:5.9.0.202009080501-r",
+        sha1 = "00a5f08c5bdc5227e69882324d1f117572105649",
     )
 
     maven_jar(