deps: Add pstore and ostruct to Gemfile

pstore and ostruct became a bundled gem since Ruby-3.5.  Therefore it should
be added to the dependency list to pass CI.

ref: https://bugs.ruby-lang.org/issues/20309

Author: tk0miya

Gemfile

@@ -44,6 +44,8 @@ gem "rbs-amber", path: "test/assets/test-gem"
 # Bundled gems
 gem "net-smtp"
 gem 'csv'
+gem 'ostruct'
+gem 'pstore'
 
 group :minitest do
   gem "minitest"

Gemfile.lock

@@ -66,11 +66,13 @@ GEM
     net-smtp (0.5.0)
       net-protocol
     nkf (0.2.0)
+    ostruct (0.6.1)
     parallel (1.26.3)
     parser (3.3.6.0)
       ast (~> 2.4.1)
       racc
     power_assert (2.0.5)
+    pstore (0.1.4)
     psych (4.0.6)
       stringio
     public_suffix (6.0.1)
@@ -174,6 +176,8 @@ DEPENDENCIES
   mutex_m
   net-smtp
   nkf
+  ostruct
+  pstore
   raap
   rake
   rake-compiler