ci_set_matrix: Don't use .get(), it hides errors

Variables that are explicitly fetched always have a value, even if it
is the empty value. However, using .get() hid the error that
shared_bindings_matrix wasn't fetching SRC_SUPERVISOR.

Author: jepler

tools/ci_set_matrix.py

@@ -189,14 +189,14 @@ def get_settings(board):
 
                     # Check frozen files to see if they are in each board
                     if file.startswith("frozen"):
-                        if file in settings.get("FROZEN_MPY_DIRS", ""):
+                        if file in settings["FROZEN_MPY_DIRS"]:
                             boards_to_build.add(board)
                             continue
 
                     # Check supervisor files
                     # This is useful for limiting workflow changes to the relevant boards
                     if file.startswith("supervisor"):
-                        if file in settings.get("SRC_SUPERVISOR", ""):
+                        if file in settings["SRC_SUPERVISOR"]:
                             boards_to_build.add(board)
                             continue