[BUG] Can not apply on conv1D layer

### Describe the bug
I try to apply the newest version of innvestigate on 1-dimensional data on tensorflow 2.15. The same model structure with conv2D can work perfectly, while I change the model to 1D and feed in 1D data, it shows "Placeholder error":

'''
InvalidArgumentError: You must feed a value for placeholder tensor 'input_layer' with dtype float and shape [?,28,1] [[{{node input_layer}}]]
'''

### Steps to reproduce the bug
This is the[ jupyter notebook script](https://github.com/niki-lei/Use-1D-data-in-innvestigate/tree/main) to replicate the bug.

### Platform information
- OS: [Windows 11]
- Python version: [3.11]
- iNNvestigate version: [ 2.0.1]
- TensorFlow version: [2.15]