[CI] redmine master version tests failed

[sanak]

Problem
redmine master version tests failed with the following bundle install error.
https://github.com/gtt-project/redmine_gtt/actions/runs/7258962536/job/19775204289?pr=270

Bundler could not find compatible versions for gem "activerecord":
  In Gemfile:
activerecord-postgis-adapter (~> 7.1.1) was resolved to 7.1.1, which depends
on
      activerecord (~> 6.1)

    rails (= 7.1.2) was resolved to 7.1.2, which depends on
      activerecord (= 7.1.2)
Error: Process completed with exit code 6.

Expectation
Gem installation and tests should be passed.

[sanak]

ActiveRecord 7.1 requires activerecord-postgis-adapter 9.x,
https://github.com/rgeo/activerecord-postgis-adapter?tab=readme-ov-file#version-9x-supports-activerecord-71

Version 9.x supports ActiveRecord 7.1

ActiveRecord 7.1
Ruby 3.0.0+
PostGIS 2.0+

so, the following CI part needs to be fixed for redmine master version.
https://github.com/gtt-project/redmine_gtt/blob/main/.github/workflows/test-postgis.yml#L90-L97

I will check other dependencies later.