reinstall: Fix the --user option in podman command

The --user option in podman command was not correctly split into two
arguments. This caused the command to fail with the following error:

```
Error: unknown flag: --user root:root
```

Signed-off-by: Omer Tuchfeld <[email protected]>

Author: omertuc

system-reinstall-bootc/src/podman.rs

@@ -16,7 +16,7 @@ pub(crate) fn command(image: &str, root_key: &Option<UserKeys>) -> Command {
         // The container needs to access the host's PID namespace to mount host directories
         "--pid=host",
         // Set the UID/GID to root overwriting any possible USER directive in the Containerfile
-        "--user root:root",
+        "--user=root:root",
         // Since https://github.com/containers/bootc/pull/919 this mount should not be needed, but
         // some reason with e.g. quay.io/fedora/fedora-bootc:41 it is still needed.
         "-v",