Fix graphgym example for activation functions

[M-Lampert]

If you choose one of the given example activation functions (swish or lrelu_03) you get the following error:

Traceback (most recent call last):
  File "C:\Users\morit\workspace\pytorch_geometric\graphgym\main.py", line 42, in <module>
    model = create_model()
  File "C:\Users\morit\.conda\envs\test\lib\site-packages\torch_geometric\graphgym\model_builder.py", line 79, in create_model
    model = GraphGymModule(dim_in, dim_out, cfg)
  File "C:\Users\morit\.conda\envs\test\lib\site-packages\torch_geometric\graphgym\model_builder.py", line 20, in __init__
    self.model = network_dict[cfg.model.type](dim_in=dim_in,
  File "C:\Users\morit\.conda\envs\test\lib\site-packages\torch_geometric\graphgym\models\gnn.py", line 147, in __init__
    self.mp = GNNStage(dim_in=dim_in, dim_out=cfg.gnn.dim_inner,
  File "C:\Users\morit\.conda\envs\test\lib\site-packages\torch_geometric\graphgym\models\gnn.py", line 69, in __init__
    layer = GNNLayer(d_in, dim_out)
  File "C:\Users\morit\.conda\envs\test\lib\site-packages\torch_geometric\graphgym\models\gnn.py", line 27, in GNNLayer
    return GeneralLayer(
  File "C:\Users\morit\.conda\envs\test\lib\site-packages\torch_geometric\graphgym\models\layer.py", line 99, in __init__
    layer_wrapper.append(register.act_dict[layer_config.act]())
  File "C:\Users\morit\.conda\envs\test\lib\site-packages\torch\nn\modules\module.py", line 1130, in _call_impl
    return forward_call(*input, **kwargs)
TypeError: forward() missing 1 required positional argument: 'x'

This happens because the classes are initialized before registering and layer.py later tries to initialize them again.
My proposal: Use partial to specify the arguments without initializing the class.

[codecov]

Codecov Report

Merging #5243 (a350d9a) into master (3d5f855) will decrease coverage by 0.11%.
The diff coverage is n/a.

@@            Coverage Diff             @@
##           master    #5243      +/-   ##
==========================================
- Coverage   83.15%   83.04%   -0.12%     
==========================================
  Files         337      337              
  Lines       18574    18574              
==========================================
- Hits        15445    15424      -21     
- Misses       3129     3150      +21     

Impacted Files	Coverage Δ
torch_geometric/utils/scatter.py	42.50% <0.00%> (-52.50%)	⬇️

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