dev_scripts: Fix bug during env build

Create the build directory first, and then add the PySide6 package in
it.

dev_scripts/env.py

@@ -608,6 +608,7 @@ def build(
     ):
         """Build a Linux environment and install Dangerzone in it."""
         build_dir = distro_build(self.distro, self.version)
+        os.makedirs(build_dir, exist_ok=True)
         version = dz_version()
         if self.distro == "fedora":
             install_deps = DOCKERFILE_BUILD_FEDORA_DEPS
@@ -672,8 +673,6 @@ def build(
             print(dockerfile)
             return
 
-        os.makedirs(build_dir, exist_ok=True)
-
         # Populate the build context.
         shutil.copy(package_src, package_dst)
         shutil.copy(git_root() / "dev_scripts" / "storage.conf", build_dir)