fix: pin ruby `bundler` gem to v`2.3.36`

[JacobMillward]

Was previously failing to build the docker image with

 => ERROR [20/25] RUN gem install bundler &&       apt-get update &&       apt-get install -y --no-install-recommends ruby-dev                                                                                                                                            3.4s
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 > [20/25] RUN gem install bundler &&       apt-get update &&       apt-get install -y --no-install-recommends ruby-dev:
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executor failed running [/bin/sh -c gem install bundler &&       apt-get update &&       apt-get install -y --no-install-recommends ruby-dev]: exit code: 1

Related Issue or Design Document

None.

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