Tweak tests, consolidate pins target validation (#21254)

buildroot/tests/STM32F103RC_btt_USB

@@ -0,0 +1,17 @@
+#!/usr/bin/env bash
+#
+# Build tests for STM32F103RC BigTreeTech (SKR Mini v1.1)
+#
+
+# exit on first failure
+set -e
+
+#
+# Build with the default configurations
+#
+restore_configs
+opt_set MOTHERBOARD BOARD_BTT_SKR_MINI_V1_1 SERIAL_PORT 1 SERIAL_PORT_2 -1
+exec_test $1 $2 "BigTreeTech SKR Mini v1.1 - Basic Configuration" "$3"
+
+# clean up
+restore_configs