Fixed some tests using deprecated FTL syntax

Author: spookylukey

fluent.runtime/tests/format/test_attributes.py

@@ -104,7 +104,7 @@ def setUp(self):
             ref-bar = { bar.missing }
             ref-baz = { baz.missing }
             ref-qux = { qux.missing }
-            attr-only
+            attr-only =
                      .attr  = Attr Only Attribute
         """))
 

fluent.runtime/tests/format/test_primitives.py

@@ -18,7 +18,7 @@ def setUp(self):
                 [Foo] Member 1
                *[Bar] Member 2
              }
-            bar
+            bar =
                 .attr = Bar Attribute
             placeable-attr   = { bar.attr }
             -baz = Baz
@@ -74,7 +74,7 @@ def setUp(self):
 
             placeable-message = { bar }Baz
 
-            baz
+            baz =
                 .attr = { bar }BazAttribute
 
             -qux = Qux