feat(gas): Support Ruby 3.4

[dazuma]

This change adds support for Ruby 3.4 to GAS, for protobuf releases.

• Pin rake-compiler and rake-compiler-dock to the latest versions (1.2.9 and 1.8.0, respectively), which have Ruby 3.4 support.
• Re-pin rake-compiler-dock images to the SHAs corresponding to version 1.8.0.
• Re-pin the gems and rake gems to the latest and greatest (1.3.0 and 13.2.1, respectively).
• rake-compiler-dock 1.8.0 images use the latest patchlevel of each Ruby version, different from previous images which used the earliest (i.e. *.0) patchlevel. This required us to update the logic that determines RUBY_CC_VERSION.
• Updated the default Ruby version lists to drop 2.7 and add 3.4.
• Added Ruby 3.4 to the CI matrix so the tests can test the 3.4 protobuf build for runtime functionality.

Also:

• Added a test to ensure cross-builds against all Ruby versions are successful.
• Updated the gas build tool to install dependencies automatically if not present. Solves a corner case where tests hang on user prompt if the bundle hasn't been installed.
• Added a cleanup between builds of different platforms. Solves a rare corner case where one platform build interferes with another.

[dazuma]

/cc @zhangskz