Introduce v3.3.0-rc6 before Gerrit v3.3 release

The recent changes in the stable-3.3 (see [1]) and the P0 bug
associated with the JGit autoGc (see [2]) have pushed the v3.3
release date by one more week, for allowing more testing before
the final release.

[1] https://gerrit-review.googlesource.com/q/hashtag:attentionset-3.3
[2] https://bugs.chromium.org/p/gerrit/issues/detail?id=13544

Change-Id: I493e5d2246b417681a770a262c614ae4196abe86
diff --git a/_posts/2020-09-07-gerrit-3.3-release-plan.md b/_posts/2020-09-07-gerrit-3.3-release-plan.md
index 0eea644..418f625 100644
--- a/_posts/2020-09-07-gerrit-3.3-release-plan.md
+++ b/_posts/2020-09-07-gerrit-3.3-release-plan.md
@@ -22,7 +22,8 @@
 | Nov 2-6   | Extra E2E testing week                             |
 | Nov 9     | Release `3.3.0-rc5`                                |
 | Nov 9-13  | "Release week" (see below)                         |
-| Nov 16    | Final release of `3.3.0`                           |
+| Nov 16    | Release `3.3.0-rc6`                                |
+| Nov 23    | Final release of `3.3.0`                           |
 
 ## Change Acceptance Policy for the Stable Branch