Bump activerecord and oracle_enhanced adapter to ~> 8.1

Both activerecord 8.1 and activerecord-oracle_enhanced-adapter 8.1
are released on RubyGems (latest 8.1.3). The previous Gemfile pin of
~> 8.0 already accepted 8.1.x; tightening it to ~> 8.1 reflects
that 8.1 is the current target Rails line for development.

The 8.0 line continues to be exercised through
gemfiles/Gemfile.activerecord-8.0 in test_gemfiles.yml.

Co-Authored-By: Claude Opus 4.7 (1M context) <noreply@anthropic.com>

Author: yahonda

Gemfile

@@ -16,8 +16,8 @@ group :test, :development do
   gem "rspec", "~> 3.1"
 
   unless ENV["NO_ACTIVERECORD"]
-    gem "activerecord", "~> 8.0"
-    gem "activerecord-oracle_enhanced-adapter", "~> 8.0"
+    gem "activerecord", "~> 8.1"
+    gem "activerecord-oracle_enhanced-adapter", "~> 8.1"
     gem "simplecov", ">= 0"
   end