fix(ProtoBuf): Component.evidence optional (#534)

fixes #422 
by reverting the unreleased
19a1530
&
acc5f3a
as discussed here:
#422 (comment)

Signed-off-by: Jan Kowalleck <[email protected]>

Author: jkowalleck

schema/bom-1.6.proto

@@ -133,8 +133,8 @@ message Component {
   repeated Component components = 21;
   // Specifies optional, custom, properties
   repeated Property properties = 22;
-  // Specifies optional license and copyright evidence. Only the first item in the optional repeated list is to be taken into account; every other item in the list is to be ignored/omitted.
-  repeated Evidence evidence = 23;
+  // Specifies optional license and copyright evidence.
+  optional Evidence evidence = 23;
   // Specifies optional release notes.
   optional ReleaseNotes releaseNotes = 24;
   // A model card describes the intended uses of a machine learning model, potential limitations, biases, ethical considerations, training parameters, datasets used to train the model, performance metrics, and other relevant data useful for ML transparency.