Fix ocaml compiler in build #4

	# General notes on github actions: Note that both the working directory
	# and environment variables generally are not shared between steps.
	name: Build using setup ocaml
	on: [push]
	jobs:
	Deploy:
	runs-on: ubuntu-latest
	steps:
	- name: Checkout the hazel repo on the current branch
	uses: actions/checkout@v2
	with:
	path: source
	- name: Add the name of the current branch to the environment as BRANCH_NAME
	uses: nelonoel/[email protected]
	- name: Set-up OCaml
	uses: ocaml/setup-ocaml@v3
	with:
	ocaml-compiler: 5.2.0
	- name: Install dependencies
	run: \|
	eval $(opam env)
	export OPAMYES=1
	opam switch import opam.export
	working-directory: ./source
	- name: Build Release
	run: \|
	opam exec dune build @src/fmt --auto-promote src --profile release
	working-directory: ./source

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