Regression: newline in quoted string for .env broken

[tracker1]

Description of the issue

When importing a .env file with a quoted string, containing a new-line character (multi-line environment variable), it is broken in 2.x (v2.0.0-rc.3), this is working correctly in 1.x (1.29.2)

Context information (for bug reports)

docker-compose.yml

version: "3.3"
services:
  test:
    image: alpine
    command: 'echo "hello $FOO!"'

.env

FOO="foo
bar
baz"

Docker Version

❯ docker version
Client: Docker Engine - Community
 Cloud integration: 1.0.17
 Version:           20.10.8
 API version:       1.41
 Go version:        go1.16.6
 Git commit:        3967b7d
 Built:             Fri Jul 30 19:54:02 2021
 OS/Arch:           linux/amd64
 Context:           default
 Experimental:      true

Server: Docker Engine - Community
 Engine:
  Version:          20.10.8
  API version:      1.41 (minimum version 1.12)
  Go version:       go1.16.6
  Git commit:       75249d8
  Built:            Fri Jul 30 19:52:10 2021
  OS/Arch:          linux/amd64
  Experimental:     false
 containerd:
  Version:          1.4.9
  GitCommit:        e25210fe30a0a703442421b0f60afac609f950a3
 runc:
  Version:          1.0.1
  GitCommit:        v1.0.1-0-g4144b63
 docker-init:
  Version:          0.19.0
  GitCommit:        de40ad0

Output - Using Compose V1 (Working)

❯ docker-compose version
docker-compose version 1.29.2, build 5becea4c
docker-py version: 5.0.0
CPython version: 3.7.10
OpenSSL version: OpenSSL 1.1.0l  10 Sep 2019

❯ docker-compose config
services:
  test:
    command: 'echo "hello foo

      bar

      baz !"'
    image: alpine
version: '3.3'

❯ docker-compose up
Starting dc1_test_1 ... done
Attaching to dc1_test_1
test_1  | hello foo
test_1  | bar
test_1  | baz !
dc1_test_1 exited with code 0

Output - Using Compose V2 (Broken)

❯ docker compose version
Docker Compose version v2.0.0-rc.3

❯ docker compose config
invalid variable name "baz\""

❯ docker compose up
invalid variable name "baz\""

Additional information

• OS; Ubuntu 20.04.2 LTS on Windows 10 x86_64
• Kernel: 5.4.72-microsoft-standard-WSL2
• Installation: Docker Desktop for Windows with WSL2 integration.

[ndeloof]

depends on joho/godotenv#118

[ndeloof]

compose v2.0.0 uses a custom fork of joho/godotenv => github.com/compose-spec/godotenv.
This fork includes joho/godotenv#118 to support multi-line values