Fix load function

[brosaplanella]

Description

Fix the load_function bug on main branch.

Fixes #1673

Type of change

Please add a line in the relevant section of CHANGELOG.md to document the change (include PR #) - note reverse order of PR #s. If necessary, also add to the list of breaking changes.

• Bug fix (non-breaking change which fixes an issue)

Key checklist:

• No style issues: $ flake8
• All tests pass: $ python run-tests.py --unit
• The documentation builds: $ cd docs and then $ make clean; make html

You can run all three at once, using $ python run-tests.py --quick.

Further checks:

• Code is commented, particularly in hard-to-understand areas
• Tests added that prove fix is effective or that feature works

[valentinsulzer]

Need to also manually increment version numbers

[codecov]

Codecov Report

Merging #1676 (84007d7) into main (6e8437f) will increase coverage by 0.00%.
The diff coverage is 100.00%.

@@           Coverage Diff           @@
##             main    #1676   +/-   ##
=======================================
  Coverage   99.26%   99.26%           
=======================================
  Files         343      343           
  Lines       18677    18680    +3     
=======================================
+ Hits        18540    18543    +3     
  Misses        137      137           

Impacted Files	Coverage Δ
pybamm/util.py	100.00% <100.00%> (ø)

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[priyanshuone6]

@brosaplanella could you also include changes from this PR to this release

[priyanshuone6]

Thanks @brosaplanella