deps: Add bundled gems to the dependencies of test app

Since Ruby 3.4, base64, bigdecimal, and drb gems have became the bundled
gem.  So they should be listed on the dependencies list.

Note: The latest activesupport now depends on them.  So it's also okay
to upgrade it to the new one.

test/app/Gemfile

@@ -10,4 +10,8 @@ gem 'bcrypt'
 
 gem 'rbs_rails', path: '../../'
 
-gem 'mutex_m'  # to run Rails6.1 under Ruby 3.4
+# to run Rails6.1 under Ruby 3.4
+gem 'base64'
+gem 'bigdecimal'
+gem 'drb'
+gem 'mutex_m'

test/app/Gemfile.lock

@@ -68,12 +68,16 @@ GEM
       tzinfo (~> 2.0)
       zeitwerk (~> 2.3)
     ast (2.4.2)
+    base64 (0.2.0)
     bcrypt (3.1.16)
+    bigdecimal (3.1.6)
     bootsnap (1.7.3)
       msgpack (~> 1.0)
     builder (3.2.4)
     concurrent-ruby (1.1.10)
     crass (1.0.6)
+    drb (2.2.0)
+      ruby2_keywords
     erubi (1.10.0)
     globalid (1.0.1)
       activesupport (>= 5.0)
@@ -133,6 +137,7 @@ GEM
       thor (~> 1.0)
     rake (13.0.3)
     rbs (3.1.0)
+    ruby2_keywords (0.0.5)
     sprockets (4.0.2)
       concurrent-ruby (~> 1.0)
       rack (> 1, < 3)
@@ -153,8 +158,11 @@ PLATFORMS
   ruby
 
 DEPENDENCIES
+  base64
   bcrypt
+  bigdecimal
   bootsnap
+  drb
   mutex_m
   psych (< 4)
   puma