Depend on importGraph via reservoir, not git.

Author: Julian

spec/fixtures/example-project/lake-manifest.json

@@ -31,7 +31,7 @@
   {"url": "https://github.com/leanprover-community/import-graph",
    "type": "git",
    "subDir": null,
-   "scope": "",
+   "scope": "leanprover-community",
    "rev": "ac7b989cbf99169509433124ae484318e953d201",
    "name": "importGraph",
    "manifestFile": "lake-manifest.json",

spec/fixtures/example-project/lakefile.toml

@@ -7,8 +7,7 @@ path = "foo"
 
 [[require]]
 name = "importGraph"
-git = "https://github.com/leanprover-community/import-graph"
-rev = "main"
+scope = "leanprover-community"
 
 [[lean_lib]]
 name = "Test"