filter out NVHPC toolchains that share name from the toolchain hierarchy

[lexming]

Fixes CI in easybuild-easyconfigs.
See easybuilders/easybuild-easyconfigs#25125

Wrong toolchain hierarchy returned by get_toolchain_hierarchy in develop:

* NVHPC/22.7-CUDA-11.7.0: [
    {'name': 'GCCcore', 'version': '11.3.0'},
    {'name': 'NVHPC', 'version': '22.7-CUDA-11.7.0'},
  ]
* NVHPC/24.9-CUDA-12.6.0: [
    {'name': 'GCCcore', 'version': '13.3.0'},
    {'name': 'NVHPC', 'version': '24.9-CUDA-12.6.0'},
  ]
* NVHPC/25.1: [
    {'name': 'GCCcore', 'version': '13.3.0'},
    {'name': 'NVHPC', 'version': '25.1'},
  ]
* NVHPC/25.3-CUDA-12.8.0: [
    {'name': 'GCCcore', 'version': '14.2.0'},
    {'name': 'NVHPC', 'version': '25.3-CUDA-12.8.0'},
  ]

Correct toolchain hierarchy returned by get_toolchain_hierarchy:

* NVHPC/22.7-CUDA-11.7.0: [
    {'name': 'GCCcore', 'version': '11.3.0'},
    {'name': 'NVHPC', 'version': '22.7-CUDA-11.7.0'},
  ]
* NVHPC/24.9-CUDA-12.6.0: [
    {'name': 'GCCcore', 'version': '13.3.0'},
    {'name': 'NVHPC', 'version': '24.9-CUDA-12.6.0'},
  ]
* NVHPC/25.1: [
    {'name': 'GCCcore', 'version': '13.3.0'},
    {'name': 'nvidia-compilers', 'version': '25.1'},
    {'name': 'NVHPC', 'version': '25.1'},
  ]
* NVHPC/25.3-CUDA-12.8.0 hierarchy: [
    {'name': 'GCCcore', 'version': '14.2.0'},
    {'name': 'nvidia-compilers', 'version': '25.3-CUDA-12.8.0'},
    {'name': 'NVHPC', 'version': '25.3-CUDA-12.8.0'},
  ]

[ocaisa]

LGTM

[ocaisa]

Going in, thanks @lexming