Fix missing entries in matrix: labels are always stored in lowercase

mlx/traceability/directives/item_pie_chart_directive.py

@@ -34,7 +34,7 @@ def make_pct(pct):
 class Match:
     """ Class for storing the label and targets for a single source item """
     def __init__(self, label):
-        self.label = label
+        self.label = label.lower()
         self.targets = {}
 
     @property
@@ -434,7 +434,7 @@ def build_table(self, app):
             subheader.get('classes').append('centered')
             row += subheader
             tbody += row
-            for source_id, match in {k: v for k, v in self.matches.items() if v.label == label}.items():
+            for source_id, match in {k: v for k, v in self.matches.items() if v.label == label.lower()}.items():
                 source = self.collection.get_item(source_id)
                 tbody += self._rows_per_source(source, match, app)
         return table