Raise more helpful errors in _dereference_path

[dstansby]

See #3387 - this doesn't fix that bug, but it should at least raise a more helpful error message.

[d-v-b]

a later PR should add a docstring that explains what this function is supposed to do

[codecov]

Codecov Report

❌ Patch coverage is 33.33333% with 4 lines in your changes missing coverage. Please review.
✅ Project coverage is 94.66%. Comparing base (c9509ee) to head (f5f6014).

Files with missing lines	Patch %	Lines
src/zarr/storage/_common.py	33.33%	4 Missing ⚠️

Additional details and impacted files

@@            Coverage Diff             @@
##             main    #3392      +/-   ##
==========================================
- Coverage   94.70%   94.66%   -0.04%     
==========================================
  Files          79       79              
  Lines        9532     9536       +4     
==========================================
  Hits         9027     9027              
- Misses        505      509       +4     

Files with missing lines	Coverage Δ
src/zarr/storage/_common.py	90.47% <33.33%> (-1.96%)	⬇️

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