Don't mount pkgmngr/ when installing trees

If we're copying from the host's /etc, the mounts get very weird as
we end up mounting over the directory we're copying from. Let's avoid
the weirdness by using the Config sandbox instead of the Context sandbox
which means we don't mount anything from the pkgmngr directory.

Fixes #2429

mkosi/__init__.py

@@ -1395,7 +1395,7 @@ def install_grub_bios(context: Context, partitions: Sequence[Partition]) -> None
 
 
 def install_tree(
-    context: Context,
+    config: Config,
     src: Path,
     dst: Path,
     *,
@@ -1413,19 +1413,19 @@ def copy() -> None:
         copy_tree(
             src, t,
             preserve=preserve,
-            use_subvolumes=context.config.use_subvolumes,
-            tools=context.config.tools(),
-            sandbox=context.sandbox,
+            use_subvolumes=config.use_subvolumes,
+            tools=config.tools(),
+            sandbox=config.sandbox,
         )
 
     if src.is_dir() or (src.is_file() and target):
         copy()
     elif src.suffix == ".tar":
-        extract_tar(src, t, tools=context.config.tools(), sandbox=context.sandbox)
+        extract_tar(src, t, tools=config.tools(), sandbox=config.sandbox)
     elif src.suffix == ".raw":
         run(
             ["systemd-dissect", "--copy-from", src, "/", t],
-            sandbox=context.sandbox(
+            sandbox=config.sandbox(
                 devices=True,
                 network=True,
                 options=["--ro-bind", src, src, "--bind", t.parent, t.parent],
@@ -1442,7 +1442,7 @@ def install_base_trees(context: Context) -> None:
 
     with complete_step("Copying in base trees…"):
         for path in context.config.base_trees:
-            install_tree(context, path, context.root)
+            install_tree(context.config, path, context.root)
 
 
 def install_skeleton_trees(context: Context) -> None:
@@ -1451,7 +1451,7 @@ def install_skeleton_trees(context: Context) -> None:
 
     with complete_step("Copying in skeleton file trees…"):
         for tree in context.config.skeleton_trees:
-            install_tree(context, tree.source, context.root, target=tree.target, preserve=False)
+            install_tree(context.config, tree.source, context.root, target=tree.target, preserve=False)
 
 
 def install_package_manager_trees(context: Context) -> None:
@@ -1477,7 +1477,7 @@ def install_package_manager_trees(context: Context) -> None:
 
     with complete_step("Copying in package manager file trees…"):
         for tree in context.config.package_manager_trees:
-            install_tree(context, tree.source, context.pkgmngr, target=tree.target, preserve=False)
+            install_tree(context.config, tree.source, context.pkgmngr, target=tree.target, preserve=False)
 
 
 def install_package_directories(context: Context) -> None:
@@ -1504,7 +1504,7 @@ def install_extra_trees(context: Context) -> None:
 
     with complete_step("Copying in extra file trees…"):
         for tree in context.config.extra_trees:
-            install_tree(context, tree.source, context.root, target=tree.target, preserve=False)
+            install_tree(context.config, tree.source, context.root, target=tree.target, preserve=False)
 
 
 def install_build_dest(context: Context) -> None: