relax ecto version constraint

[NikitaNaumenko]

Make it possible to use Ecto higher version than 3.8.3

[chasers]

We need ecto 3.9.5+ for Erlang 26 it seems.

[scvalex]

I just ran into this in a new Phoenix project. It looks like the latest ecto_sql depends on ecto ~> 3.10.0, so adding etso to the project fails unless you downgrade ecto_sql.

Failed to use "ecto" (version 3.10.3) because
  ecto_sql (version 3.10.2) requires ~> 3.10.0
  etso (version 1.1.0) requires ~> 3.8.3
  phoenix_live_dashboard (version 0.8.3) requires ~> 3.6.2 or ~> 3.7
  mix.lock specifies 3.10.3

[scvalex]

In case anybody else runs into this, you can override the ecto version in mix.exs with the following. This applies to indirect dependencies as well, so it silences the above failure about ecto_sql and etso wanting different versions.

{:ecto, "~> 3.10.3", override: true},