[SPARK-37284][BUILD] Upgrade Jekyll to 4.2.1

### What changes were proposed in this pull request?

Jekyll 4.2.1 was released in September, which includes the fix of a regression bug.
https://github.com/jekyll/jekyll/releases/tag/v4.2.1

### Why are the changes needed?

To keep it stable.

### Does this PR introduce _any_ user-facing change?

No.

### How was this patch tested?

CIs.

Closes #34552 from sarutak/upgrade-jekyll-4.2.1.

Authored-by: Kousuke Saruta <sarutak@oss.nttdata.com>
Signed-off-by: Dongjoon Hyun <dongjoon@apache.org>

docs/Gemfile

@@ -17,7 +17,7 @@
 
 source "https://rubygems.org"
 
-gem "jekyll", "4.2.0"
+gem "jekyll", "4.2.1"
 gem "rouge", "3.26.0"
 gem "jekyll-redirect-from", "0.16.0"
 gem "webrick", "1.7"

docs/Gemfile.lock

@@ -1,20 +1,20 @@
 GEM
   remote: https://rubygems.org/
   specs:
-    addressable (2.7.0)
+    addressable (2.8.0)
       public_suffix (>= 2.0.2, < 5.0)
     colorator (1.1.0)
-    concurrent-ruby (1.1.8)
+    concurrent-ruby (1.1.9)
     em-websocket (0.5.2)
       eventmachine (>= 0.12.9)
       http_parser.rb (~> 0.6.0)
     eventmachine (1.2.7)
-    ffi (1.14.2)
+    ffi (1.15.4)
     forwardable-extended (2.6.0)
     http_parser.rb (0.6.0)
-    i18n (1.8.9)
+    i18n (1.8.11)
       concurrent-ruby (~> 1.0)
-    jekyll (4.2.0)
+    jekyll (4.2.1)
       addressable (~> 2.4)
       colorator (~> 1.0)
       em-websocket (~> 0.5)
@@ -35,36 +35,36 @@ GEM
       sassc (> 2.0.1, < 3.0)
     jekyll-watch (2.2.1)
       listen (~> 3.0)
-    kramdown (2.3.0)
+    kramdown (2.3.1)
       rexml
     kramdown-parser-gfm (1.1.0)
       kramdown (~> 2.0)
     liquid (4.0.3)
-    listen (3.4.1)
+    listen (3.7.0)
       rb-fsevent (~> 0.10, >= 0.10.3)
       rb-inotify (~> 0.9, >= 0.9.10)
     mercenary (0.4.0)
     pathutil (0.16.2)
       forwardable-extended (~> 2.6)
     public_suffix (4.0.6)
-    rb-fsevent (0.10.4)
+    rb-fsevent (0.11.0)
     rb-inotify (0.10.1)
       ffi (~> 1.0)
-    rexml (3.2.4)
+    rexml (3.2.5)
     rouge (3.26.0)
     safe_yaml (1.0.5)
     sassc (2.4.0)
       ffi (~> 1.9)
     terminal-table (2.0.0)
       unicode-display_width (~> 1.1, >= 1.1.1)
-    unicode-display_width (1.7.0)
+    unicode-display_width (1.8.0)
     webrick (1.7.0)
 
 PLATFORMS
   ruby
 
 DEPENDENCIES
-  jekyll (= 4.2.0)
+  jekyll (= 4.2.1)
   jekyll-redirect-from (= 0.16.0)
   rouge (= 3.26.0)
   webrick (= 1.7)