utils/misc: raise an exception if a shader is not found
utils/misc: raise an exception if a shader is not found

pkgutil.get_data() returns None sometimes:

    >>> import pkgutil
    >>> pkgutil.get_data("x", "y")
    >>>

And at other times it tracebacks:

    >>> import pkgutil
    >>> pkgutil.get_data("pynodegl_utils.examples.shaders", "no")
    Traceback (most recent call last):
      File "<stdin>", line 1, in <module>
      File "/usr/lib/python3.10/pkgutil.py", line 639, in get_data
        return loader.get_data(resource_name)
      File "<frozen importlib._bootstrap_external>", line 1073, in get_data
    FileNotFoundError: [Errno 2] No such file or directory: '/mnt/work/src/node.gl/pynodegl-utils/pynodegl_utils/examples/shaders/no'

In order to be consistent, we make sure a proper exception is always
raised.

gopro/gopro-lib-node.gl,gopro/gopro-lib-node.gl,gopro/gopro-lib-node.gl,gopro/gopro-lib-node.gl