Update dependency flatware-rspec to v2.4.0 (mastodon#38327)

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

Author: renovate[bot]

Gemfile.lock

@@ -251,12 +251,14 @@ GEM
     ffi-compiler (1.3.2)
       ffi (>= 1.15.5)
       rake
-    flatware (2.3.4)
+    flatware (2.4.0)
+      benchmark
       drb
+      logger
       thor (< 2.0)
-    flatware-rspec (2.3.4)
-      flatware (= 2.3.4)
-      rspec (>= 3.6)
+    flatware-rspec (2.4.0)
+      flatware (= 2.4.0)
+      rspec (>= 3.8)
     fog-core (2.6.0)
       builder
       excon (~> 1.0)