Protobuf

Ruby
* Fixed memory leak of Ruby arena objects (8461)

C++
* Remove the ::pb namespace (alias) (8423)

Ruby
* Fix unbounded memory growth for Ruby <2.7 (8429)
* Fixed message equality in cases where the message type is different (8434)

Ruby
* Fixed bug in string comparison logic (8386)

Ruby
* Fixed quadratic memory use in array append (8379)

PHP
* Fixed quadratic memory use in array append (8379)

C++
* Do not disable RTTI by default in the CMake build (8377)

Ruby
* Fixed SEGV when users pass nil messages (8363)
* Fixed quadratic memory usage when appending to arrays (8364)

C++
* Create a CMake option to control whether or not RTTI is enabled (8361)

PHP
* read_property() handler is not supposed to return NULL (8362)

Ruby
* Ruby <2.7 now uses WeakMap too, which prevents memory leaks. (8341)