Tolerate some "none-looking" names in variant setting

With the change, all the following would point to the None pkgman:

```
package_manager: null
package_manager: None
package_manager: ''
package_manager: 'None'
package_manager: 'none'
```

Author: linsword13

lib/ramble/ramble/application.py

@@ -130,6 +130,15 @@ def _get_phase_func_wrapper(workspace, phase_func, phase_name):
     return profiler(phase_func)
 
 
+def _canonical_none(maybe_none):
+    """Convert a small set of "none-looking" inputs to None"""
+    if maybe_none == "":
+        return None
+    if isinstance(maybe_none, str) and maybe_none.lower() == "none":
+        return None
+    return maybe_none
+
+
 class ApplicationBase(metaclass=ApplicationMeta):
     name = None
     _builtin_name = NS_SEPARATOR.join(("builtin", "{name}"))
@@ -280,8 +289,8 @@ def set_variants(self, variants):
 
     def _set_package_manager(self):
         if namespace.package_manager in self.variants:
-            pkgman_name = self.expander.expand_var(
-                self.variants[namespace.package_manager], typed=True
+            pkgman_name = _canonical_none(
+                self.expander.expand_var(self.variants[namespace.package_manager], typed=True)
             )
 
             if pkgman_name is not None:
@@ -310,18 +319,18 @@ def _set_package_manager(self):
 
     def _set_workflow_manager(self):
         if namespace.workflow_manager in self.variants:
-            workflow_name = self.expander.expand_var(
-                self.variants[namespace.workflow_manager], typed=True
+            wm_name = _canonical_none(
+                self.expander.expand_var(self.variants[namespace.workflow_manager], typed=True)
             )
 
-            if workflow_name is not None:
+            if wm_name is not None:
                 try:
                     wfman_type = ramble.repository.ObjectTypes.workflow_managers
-                    self.workflow_manager = ramble.repository.get(workflow_name, wfman_type).copy()
+                    self.workflow_manager = ramble.repository.get(wm_name, wfman_type).copy()
                     self.workflow_manager.set_application(self)
                 except ramble.repository.UnknownObjectError:
                     logger.die(
-                        f"{workflow_name} is not a valid workflow manager. "
+                        f"{wm_name} is not a valid workflow manager. "
                         "Valid workflow managers can be listed via:\n"
                         "\tramble list --type workflow_managers"
                     )

lib/ramble/ramble/test/package_manager_functionality/package_manager_general.py

@@ -0,0 +1,62 @@
+# Copyright 2022-2025 The Ramble Authors
+#
+# Licensed under the Apache License, Version 2.0 <LICENSE-APACHE or
+# https://www.apache.org/licenses/LICENSE-2.0> or the MIT license
+# <LICENSE-MIT or https://opensource.org/licenses/MIT>, at your
+# option. This file may not be copied, modified, or distributed
+# except according to those terms.
+
+import os
+
+import pytest
+
+import ramble.workspace
+from ramble.main import RambleCommand, RambleCommandError
+
+workspace = RambleCommand("workspace")
+
+pytestmark = pytest.mark.usefixtures(
+    "mutable_config",
+    "mutable_mock_workspace_path",
+)
+
+
+@pytest.mark.maybeslow
+@pytest.mark.parametrize(
+    "pkgman_name,expect_success_setup",
+    [
+        ("none", True),
+        (None, True),
+        ("", True),
+        ("spack", True),
+        ("non-existent-pkgman", False),
+    ],
+)
+def test_package_manager_names(pkgman_name, expect_success_setup):
+    ws_name = f"test-{pkgman_name}"
+    ws = ramble.workspace.create(ws_name)
+    workspace(
+        "manage",
+        "experiments",
+        "hostname",
+        "-p",
+        pkgman_name,
+        "--wf",
+        "local",
+        "-v",
+        "n_nodes=1",
+        "-v",
+        "processes_per_node=1",
+        "-v",
+        "mpi_command=''",
+        "-v",
+        "batch_submit=''",
+        global_args=["-w", ws_name],
+    )
+    ws._re_read()
+    if expect_success_setup:
+        workspace("setup", "--dry-run", global_args=["-D", ws.root])
+        assert os.path.isfile(os.path.join(ws.log_dir, "setup.latest.out"))
+    else:
+        with pytest.raises(RambleCommandError):
+            workspace("setup", "--dry-run", global_args=["-D", ws.root])