build downstream spl bpf programs for tests (backport #19851) (#19887)

Co-authored-by: Justin Starry <justin@solana.com>

scripts/build-downstream-projects.sh

@@ -68,6 +68,7 @@ spl() {
 
     $cargo build
     $cargo test
+    $cargo_build_bpf
     $cargo_test_bpf
   )
 }