chore: update podspec version to 1.2.6

Update version to match the latest git tag (1.2.6) which includes
all recent Objective-C bridge method additions for subscription
management.

🤖 Generated with [Claude Code](https://claude.com/claude-code)

Co-Authored-By: Claude <noreply@anthropic.com>

Author: hyochan

openiap.podspec

@@ -1,6 +1,6 @@
 Pod::Spec.new do |s|
   s.name             = 'openiap'
-  s.version          = '1.2.4'
+  s.version          = '1.2.6'
   s.summary          = 'OpenIAP - Modern Swift library for in-app purchases'
   s.description      = <<-DESC
     OpenIAP is a modern Swift library for handling in-app purchases using StoreKit 2.