[CI] Updates default Docker ruby to 3.1

Author: picandocodigo

.ci/Dockerfile

@@ -1,4 +1,4 @@
-ARG RUBY_TEST_VERSION=2.7
+ARG RUBY_TEST_VERSION=3.1
 FROM ruby:${RUBY_TEST_VERSION}
 
 # Default UID/GID to 1000

.ci/make.sh

@@ -37,7 +37,7 @@ output_folder=".ci/output"
 codegen_folder=".ci/output"
 OUTPUT_DIR="$repo/${output_folder}"
 REPO_BINDING="${OUTPUT_DIR}:/sln/${output_folder}"
-RUBY_TEST_VERSION=${RUBY_TEST_VERSION-2.7}
+RUBY_TEST_VERSION=${RUBY_TEST_VERSION-3.1}
 WORKFLOW=${WORKFLOW-staging}
 mkdir -p "$OUTPUT_DIR"