Update dependency doorkeeper to v5.6.8 (#28177)

Co-authored-by: renovate[bot] <29139614+renovate[bot]@users.noreply.github.com>

Gemfile.lock

@@ -245,7 +245,7 @@ GEM
     docile (1.4.0)
     domain_name (0.5.20190701)
       unf (>= 0.0.5, < 1.0.0)
-    doorkeeper (5.6.7)
+    doorkeeper (5.6.8)
       railties (>= 5)
     dotenv (2.8.1)
     dotenv-rails (2.8.1)
@@ -617,7 +617,7 @@ GEM
     redlock (1.3.2)
       redis (>= 3.0.0, < 6.0)
     regexp_parser (2.8.2)
-    reline (0.4.0)
+    reline (0.4.1)
       io-console (~> 0.5)
     request_store (1.5.1)
       rack (>= 1.4)