[gd32][build] skip package precheck during gd32vw553h clean

[Copilot]

The riscv-none Actions job was failing in the GD32VW553H-EVAL BSP cleanup phase, not during compilation. scons -c still executed the BSP package availability check, so CI exited after successful build/dist steps when packages were no longer present.

• Root cause

  • bsp/gd32/risc-v/gd32vw553h-eval/SConstruct registers bsp_pkg_check() as a pre-build action.
  • That check ran unconditionally, including for scons -c, making cleanup depend on fetched packages.

• Change

  • Short-circuit bsp_pkg_check() when SCons is running in clean mode.
  • Keep the existing package guard intact for normal builds.

• Impact

  • Cleanup no longer fails after CI build/dist flows remove or omit packages.
  • Build behavior is unchanged: missing required packages still stop real builds early.

• Code

  def bsp_pkg_check():
      if GetOption('clean'):
          return
  
      need_update = not packages_available(os.path.abspath('.'), ['gd32-riscv-series-latest'])

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