project: use new Manifest.encoding constant (utf-8) to read manifest

Fixes issue reported in PR #710 where most places are hardcoded to
'utf-8' while this one is (Windows) locale-dependent. In the future, we
may want to make this more flexible but the most urgent fix is
consistency: with this commit, manifest decoding should be hardcoded to
'utf-8' everywhere.

Signed-off-by: Marc Herbert <marc.herbert@intel.com>

src/west/app/project.py

@@ -321,7 +321,7 @@ def bootstrap(self, args) -> Path:
         # Parse the manifest to get "self: path:", if it declares one.
         # Otherwise, use the URL. Ignore imports -- all we really
         # want to know is if there's a "self: path:" or not.
-        manifest = Manifest.from_data(temp_manifest.read_text(),
+        manifest = Manifest.from_data(temp_manifest.read_text(encoding=Manifest.encoding),
                                       import_flags=ImportFlag.IGNORE)
         if manifest.yaml_path:
             manifest_path = manifest.yaml_path