Undrop ruby 2.6 (#32160)

Rakefile

@@ -144,7 +144,7 @@ task 'gem:native', [:plat] do |t, args|
   verbose = ENV['V'] || '0'
 
   grpc_config = ENV['GRPC_CONFIG'] || 'opt'
-  ruby_cc_versions = ['3.2.0', '3.1.0', '3.0.0', '2.7.0'].join(':')
+  ruby_cc_versions = ['3.2.0', '3.1.0', '3.0.0', '2.7.0', '2.6.10'].join(':')
   selected_plat = "#{args[:plat]}"
 
   # use env variable to set artifact build paralellism

tools/dockerfile/distribtest/ruby_stretch_x64_ruby_2_6.current_version

@@ -0,0 +1 @@
+us-docker.pkg.dev/grpc-testing/testing-images-public/ruby_stretch_x64_ruby_2_6:4b215aa6d7029aaa63679881d54b8ca620e2d775@sha256:b9cc471908386767a9dbf3baffb7a67aa93c4cd1057c4ba8572c691c8ba4b3e6

tools/dockerfile/distribtest/ruby_stretch_x64_ruby_2_6/Dockerfile

@@ -0,0 +1,42 @@
+# Copyright 2015 gRPC authors.
+#
+# Licensed under the Apache License, Version 2.0 (the "License");
+# you may not use this file except in compliance with the License.
+# You may obtain a copy of the License at
+#
+#     http://www.apache.org/licenses/LICENSE-2.0
+#
+# Unless required by applicable law or agreed to in writing, software
+# distributed under the License is distributed on an "AS IS" BASIS,
+# WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+# See the License for the specific language governing permissions and
+# limitations under the License.
+
+FROM debian:stretch
+
+# Install Git and basic packages.
+RUN apt-get update && apt-get install -y \
+  gnupg2 \
+  procps \
+  curl \
+  gcc && apt-get clean
+
+#==================
+# Ruby dependencies
+
+# Install rvm
+RUN gpg2 --keyserver hkp://keyserver.ubuntu.com --recv-keys 409B6B1796C275462A1703113804BB82D39DC0E3 7D2BAF1CF37B13E2069D6956105BD0E739499BDB
+RUN \curl -sSL https://get.rvm.io | bash -s stable
+
+# Install Ruby 2.6
+RUN /bin/bash -l -c "rvm install ruby-2.6.5"
+RUN /bin/bash -l -c "rvm use --default ruby-2.6.5"
+RUN /bin/bash -l -c "echo 'gem: --no-document' > ~/.gemrc"
+RUN /bin/bash -l -c "echo 'export PATH=/usr/local/rvm/bin:$PATH' >> ~/.bashrc"
+RUN /bin/bash -l -c "echo 'rvm --default use ruby-2.6.5' >> ~/.bashrc"
+RUN /bin/bash -l -c "gem install bundler --no-document"
+
+RUN mkdir /var/local/jenkins
+
+# Define the default command.
+CMD ["bash"]

tools/run_tests/artifacts/distribtest_targets.py

@@ -431,6 +431,12 @@ def targets():
         PythonDistribTest('linux', 'x64', 'arch', source=True),
         PythonDistribTest('linux', 'x64', 'ubuntu2004', source=True),
         # Ruby
+        RubyDistribTest('linux',
+                        'x64',
+                        'stretch',
+                        ruby_version='ruby_2_6',
+                        source=True,
+                        presubmit=True),
         RubyDistribTest('linux',
                         'x64',
                         'stretch',