scripts: Read yaml files using utf-8 encoding

By default Windows does not use utf-8 encoding for reading files,
set is explicitly.

Signed-off-by: Pieter De Gendt <pieter.degendt@basalte.be>
diff --git a/scripts/list_boards.py b/scripts/list_boards.py
index 4bc83df..bf71658 100755
--- a/scripts/list_boards.py
+++ b/scripts/list_boards.py
@@ -183,7 +183,7 @@
 def load_v2_boards(board_name, board_yml, systems):
     boards = []
     if board_yml.is_file():
-        with board_yml.open('r') as f:
+        with board_yml.open('r', encoding='utf-8') as f:
             b = yaml.load(f.read(), Loader=SafeLoader)
 
         try: