Add Ruby 3.1 to Circle tests (#2129)

Remove Aliases in "config/secrets.yml" to support Ruby 3.1 + Rails 6.1

Ruby 3.1 ships with Psych 4. Psych 4 switched it's default YAML parsing mode to
a safer mode, including not allowing aliases. This broke parsing of
"secrets.yml" in Rails, if the secrets file contains any aliases.

Some discussion: https://bugs.ruby-lang.org/issues/17866

Rails PR 42687 implemented a fix, and that fix was included in Rails 7 here:
rails/rails@0ebb708

It was also included in the Rails 6-1-stable branch here:
rails/rails@aac3edb

But that commit happened after Rails 6.1.4 was published, and no patch-level
releases have been made for Rails 6.1 since that commit. Only security-level
releases have been published. I assume if Rails 6.1.5 is released it will
contain the fix.

Until Rails 6.1.5 is released, the best option to be able to test Ruby 3.1
against Rails 6.1 apps is probably to just eliminate any aliases in yaml files
that Rails uses.

Using new CircleCI image "cimg/ruby"

.circleci/config.yml

@@ -2,7 +2,7 @@
 version: 2.1
 
 orbs:
-  browser-tools: circleci/browser-tools@1.2.3
+  browser-tools: circleci/browser-tools@1.2.4
 
 commands:
   shared_steps:
@@ -86,7 +86,7 @@ jobs:
     <<: *default_job
     steps:
       - shared_steps
-      # Run the tests against the versions of Rails that support Ruby 3
+      # Run the tests against the versions of Rails that support Ruby 3.0
       - run: bundle exec appraisal install
       - run: bundle exec appraisal rails60 rspec
       - run: bundle exec appraisal rails61 rspec
@@ -102,10 +102,30 @@ jobs:
           POSTGRES_DB: ruby30
           POSTGRES_PASSWORD: ""
 
+  ruby-31:
+    <<: *default_job
+    steps:
+      - shared_steps
+      # Run the tests against the versions of Rails that support Ruby 3.1
+      - run: bundle exec appraisal install
+      - run: bundle exec appraisal rails61 rspec
+    docker:
+      - image: cimg/ruby:3.1-browsers
+        environment:
+          PGHOST: localhost
+          PGUSER: administrate
+          RAILS_ENV: test
+      - image: postgres:10.1-alpine
+        environment:
+          POSTGRES_USER: administrate
+          POSTGRES_DB: ruby31
+          POSTGRES_PASSWORD: ""
+
 workflows:
   version: 2
   multiple-rubies:
     jobs:
+      - ruby-31
       - ruby-30
       - ruby-27
       - ruby-26

spec/example_app/config/secrets.yml

@@ -1,15 +1,11 @@
-default: &default
-  secret_key_base: <%= ENV["SECRET_KEY_BASE"] %>
-
 development:
-  <<: *default
   secret_key_base: 1a022e4f335d24af3d6bd622b9daef5a44808afbe16d4f1c8bed03675ab91ecd9c76ddc1a30f3fbb668b02c00abcba2ecc3714c95943b8f4af86289a2a46d5e1
 
 test:
   secret_key_base: test_secret
 
 staging:
-  <<: *default
+  secret_key_base: <%= ENV["SECRET_KEY_BASE"] %>
 
 production:
-  <<: *default
+  secret_key_base: <%= ENV["SECRET_KEY_BASE"] %>