Empty env vars not being set in container jobs

Describe the bug
When you set container env vars, if the env var is an empty string, the env var doesn't get set. This is incorrect as for some purposes there is a logical difference between an env var not being set and an env var being set to an empty string.

To Reproduce

jobs:
  test_env_var_bug:
    name: Test Empty Env Var Bug
    runs-on: ubuntu-latest
    container:
      image: node:18
      env:
        FOO_ONE: ""
        FOO_TWO: "I show up!"
    steps:
    - name: TEST
      run: env | grep "FOO"

Console output:

Expected behavior
I'd expect that both env vars are set in the env and that when you run env you'd see something like this:=

Console output:

Run env | grep "FOO"
FOO_ONE=
FOO_TWO=I show up!

Runner Version and Platform

'2.311.0'
ubuntu-latest

Start by reproducing the issue with the YAML workflow and container image shown in the report, then trace the runner's container-job environment handling. Done means both FOO_ONE and FOO_TWO appear in the container environment, with FOO_ONE retaining an empty value.