Ruby 2.3 needs older Bundler to work

[olleolleolle]

Installing Bundler
  /opt/hostedtoolcache/Ruby/2.3.8/x64/bin/gem install bundler -v ~> 2
  ERROR:  Error installing bundler:
  	bundler requires Ruby version >= 2.6.0.
  Took   0.72 seconds

Details

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an earlier, non-failed build had this message: so, perhaps for this version, pinning to 2.3.26 could work?

Installing Bundler
  /opt/hostedtoolcache/Ruby/2.3.8/x64/bin/gem install bundler -v ~> 2
  Successfully installed bundler-2.3.26
  1 gem installed
  Took   0.53 seconds