Volume definition required for single use volumes

**Describe the bug**

Podman-compose always requires volume labels to be defined in the top-level config, otherwise it will stop and give the error `RuntimeError: volume [volume_name] not defined in top level`. This is wrong, since the [spec](https://github.com/compose-spec/compose-spec/blob/master/spec.md#volumes) says this is not needed for volumes that are used in a single service:

```
If the mount is a host path and is only used by a single service, it can be declared as part of the service definition. To reuse a volume across multiple services, a named volume must be declared in the [top-level volumes key](https://github.com/compose-spec/compose-spec/blob/master/07-volumes.md).
```

**To Reproduce**
Steps to reproduce the behavior:
1. Try to run a docker-compose.yml with volume labels such as the following:

```
services:
frontend:
image: busybox
volumes:
- testdir:/home/user:z
```

**Expected behavior**
It runs

**Actual behavior**
It gives the error `RuntimeError: volume [testdir] not defined in top level`. Adding the following fixes the error. But this should not be required.
```
volumes:
testdir:
```

**Output**

```
$ podman-compose version
podman-compose version: 1.0.6
['podman', '--version', '']
using podman version: 4.6.1
podman-compose version 1.0.6
podman --version
podman version 4.6.1
exit code: 0

$ podman-compose up
...
podman-compose version: 1.0.6
['podman', '--version', '']
using podman version: 4.6.1
Traceback (most recent call last):
File "/usr/bin/podman-compose", line 33, in
sys.exit(load_entry_point('podman-compose==1.0.6', 'console_scripts', 'podman-compose')())
^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
File "/usr/lib/python3.11/site-packages/podman_compose.py", line 2940, in main
podman_compose.run()
File "/usr/lib/python3.11/site-packages/podman_compose.py", line 1420, in run
self._parse_compose_file()
File "/usr/lib/python3.11/site-packages/podman_compose.py", line 1627, in _parse_compose_file
raise RuntimeError(
RuntimeError: volume [testdir] not defined in top level
```

**Environment:**
- OS: Linux
- podman version: 4.6.1
- podman compose version: 1.0.6

**Additional context**

The bug is introduced in https://github.com/containers/podman-compose/commit/154a51245ff2c5c8c3690d3a0035b710b69d0c3d.

ref: #746