Make setuptools_scm optional, even if installed in editable mode.

Author: dihm

labscript/__version__.py

@@ -4,16 +4,22 @@
 except ImportError:
     import importlib_metadata
 
-VERSION_SCHEME = {
-    "version_scheme": "release-branch-semver",
-    "local_scheme": "node-and-date",
-}
-
 root = Path(__file__).parent.parent
 if (root / '.git').is_dir():
-    
-    from setuptools_scm import get_version
-    __version__ = get_version(root, **VERSION_SCHEME)
+    try:
+        from setuptools_scm import get_version
+        VERSION_SCHEME = {
+            "version_scheme": "release-branch-semver",
+            "local_scheme": "node-and-date",
+        }
+        scm_version = get_version(root, **VERSION_SCHEME)
+    except ImportError:
+        scm_version = None
+else:
+    scm_version = None
+
+if scm_version is not None:
+    __version__ = scm_version
 else:
     try:
         __version__ = importlib_metadata.version(__package__)