Add a ruby 3.0.0 distrib test

tools/dockerfile/distribtest/ruby_jessie_x64_ruby_3_0/Dockerfile

@@ -0,0 +1,40 @@
+# Copyright 2020 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:jessie
+
+# Install Git and basic packages.
+RUN apt-get update && apt-get install -y \
+  curl \
+  gcc && apt-get clean
+
+#==================
+# Ruby dependencies
+
+# Install rvm
+RUN gpg --keyserver hkp://keys.gnupg.net --recv-keys 409B6B1796C275462A1703113804BB82D39DC0E3 7D2BAF1CF37B13E2069D6956105BD0E739499BDB
+RUN \curl -sSL https://get.rvm.io | bash -s stable
+
+# Install Ruby 3.0
+RUN /bin/bash -l -c "rvm install ruby-3.0.0"
+RUN /bin/bash -l -c "rvm use --default ruby-3.0.0"
+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-3.0.0' >> ~/.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

@@ -363,6 +363,7 @@ def targets():
         RubyDistribTest('linux', 'x64', 'jessie', ruby_version='ruby_2_5'),
         RubyDistribTest('linux', 'x64', 'jessie', ruby_version='ruby_2_6'),
         RubyDistribTest('linux', 'x64', 'jessie', ruby_version='ruby_2_7'),
+        RubyDistribTest('linux', 'x64', 'jessie', ruby_version='ruby_3_0'),
         RubyDistribTest('linux',
                         'x64',
                         'jessie',