chore: update a2a.proto to v1.0.0 tag

The proto definitions did not change betwee the previous commit (601c408)
and the v1.0.0 tag.

Update the tracking comment to reference the
official release tag.

Author: jmesnil

spec-grpc/src/main/proto/a2a.proto

@@ -9,7 +9,7 @@ import "google/protobuf/empty.proto";
 import "google/protobuf/struct.proto";
 import "google/protobuf/timestamp.proto";
 
-// From commit 601c408
+// From tag v1.0.0
 
 option csharp_namespace = "Lf.A2a.V1";
 option go_package = "google.golang.org/lf/a2a/v1";