Cannot retrieve and display Github env setup in previous step - github

Question

I am trying to setup a variable in my CI pipeline that I will reuse later (eventually in another job, which I don't know if possible since I don't know if jobs shares variables.. but this is another problem). My pipeline is:
name: CI
on:
pull_request:
branches:
- main
jobs:
test-job:
runs-on: ubuntu-latest
name: test-job
steps:
- name: setup env variable
run: |
BRANCH_NAME=`echo "${{github.head_ref}}"'`
echo "BRANCH_NAME=$BRANCH_NAME" >> $GITHUB_ENV
echo ${{ env.BRANCH_NAME }}
that last echo doesn't show anything unfortunately. I am sure that BRANCH_NAME is correctly set because before pushing it into the $GITHUB_ENV" I did echo it and it contains data. Plus you can see the name of the branch in the console logs.
Console logs from Github are the following:
1. Run BRANCH_NAME=`echo "test_branch"'`
2. BRANCH_NAME=test_branch >> /home/runner/work/_temp/_runner_file_commands/set_env_9eeeac39-f573-4079-ba62-e1c2019f7aff
3.
So, that final echo ${{ env.BRANCH_NAME }} gives no result. What am I missing?
UPDATE:
As suggested in the comments, I started using workflow variables, in such a way that they are available throughout all the jobs.
The initial setup becomes:
name: CI
on:
pull_request:
branches:
- main
env:
BRANCH_NAME: ""
jobs:
...
I don't like the fact I need to give those variables an empty string value as placeholder and would have preferred declaring and assigning them in one of the jobs itself.. but still. So, now variables are declared before the jobs section, how do I assign a value to them in one of my steps? Meaning, I need to replace the
echo "BRANCH_NAME=$BRANCH_NAME" >> $GITHUB_ENV
tried already
echo "BRANCH_NAME=$BRANCH_NAME >> ${{ env.BRANCH_NAME }}
or
${{ env.BRANCH_NAME }}=$BRANCH_NAME
but both ways don't work.