rustPlatform.importCargoLock: fix [package] section handling

Members of the [package] table in Cargo.toml can be either subtables, or
values like strings and bools. Python is happy to check for membership
of "workspace" in a string, since Python strings are iterables, but if
the value is a bool, Python will throw an exception.

pkgs/build-support/rust/import-cargo-lock.nix

···
 
   # Replaces values inherited by workspace members.
   replaceWorkspaceValues = writers.writePython3 "replace-workspace-values"
-    { libraries = with python3Packages; [ tomli tomli-w ]; flakeIgnore = [ "E501" ]; }
+    { libraries = with python3Packages; [ tomli tomli-w ]; flakeIgnore = [ "E501" "W503" ]; }
     (builtins.readFile ./replace-workspace-values.py);
 
   # Fetch and unpack a crate.

pkgs/build-support/rust/replace-workspace-values.py

···
 def replace_key(
     workspace_manifest: dict[str, Any], table: dict[str, Any], section: str, key: str
 ) -> bool:
-    if "workspace" in table[key] and table[key]["workspace"] is True:
+    if (
+        isinstance(table[key], dict)
+        and "workspace" in table[key]
+        and table[key]["workspace"] is True
+    ):
         print("replacing " + key)
 
         replaced = table[key]

pkgs/build-support/rust/test/import-cargo-lock/default.nix

···
   v1 = callPackage ./v1 { };
   gitDependencyWorkspaceInheritance = callPackage ./git-dependency-workspace-inheritance {
     replaceWorkspaceValues = writers.writePython3 "replace-workspace-values"
-      { libraries = with python3Packages; [ tomli tomli-w ]; flakeIgnore = [ "E501" ]; }
+      { libraries = with python3Packages; [ tomli tomli-w ]; flakeIgnore = [ "E501" "W503" ]; }
       (builtins.readFile ../../replace-workspace-values.py);
   };
 }

pkgs/build-support/rust/test/import-cargo-lock/git-dependency-workspace-inheritance/crate.toml

···
 [package]
+name = "im_using_workspaces"
 version = { workspace = true }
+publish = false
+keywords = [
+    "workspace",
+    "other_thing",
+    "third_thing",
+]
 
 [dependencies]
 foo = { workspace = true, features = ["cat"] }

pkgs/build-support/rust/test/import-cargo-lock/git-dependency-workspace-inheritance/want.toml

···
 [package]
+name = "im_using_workspaces"
 version = "1.0.0"
+publish = false
+keywords = [
+    "workspace",
+    "other_thing",
+    "third_thing",
+]
 
 [dependencies]
 bar = "1.0.0"