Setup Erlang/OTP in CI using a GitHub Action

[bjosv]

This PR also adds OTP-26 and 27 to the build matrix which triggered some faults, now fixed:

• Disable warning about unknown functions or types in Dialyzer
  Starting with OTP-26 the unknown function or type warning is on by default. This will make Dialyzer complain about any types for which it has no definitions or can't infer.

  Gives warnings for Unknown type supervisor:sup_ref/0 which does not seem to be an exported type. (but also Unknown function ct:pal/1, Unknown function eunit:test/1)

• Update test empty_string_host_t() for OTP 26
  OTP-18543 which is introduced in OTP-26 states: "Looking up, connecting to and sending to a host with an empty name is now handled by trying to look up the address of the root domain, which fails. Previously some of these operations caused an internal exception, which contradicted type specifications."

[bjosv]

OK, lets disable the warning to start with then.