Fix nightly dependencies workflow and update to use python 3.14

[SarahRo]

Description

Updates the nightly-dependencies workflow to use python 3.14 as the latest supported version of pytho.

Fixes the following issue: The workflow currently fails since the main branch of PyBaMM depends on a version of pybammsolvers that doesn't have a PyPI release.

To fix this, pybammsolvers is now also installed from the main branch of the PyBaMM repository and the relevant dependencies were added.

Successful workflow run: https://github.com/pybop-team/PyBOP/actions/runs/37931093677

Fixes # (issue)

Type of change

Please add a line in the relevant section of CHANGELOG.md to document the change (include PR #).

Important checks:

Please confirm the following before marking the PR as ready for review:

• No style issues: $ pre-commit run or $ nox -s pre-commit (see CONTRIBUTING.md for how to set this up to run automatically when committing locally, in just two lines of code)
• All tests pass: nox -s tests
• The documentation builds: nox -s doctest
• Code is commented for hard-to-understand areas
• Tests added that prove fix is effective or that feature works

[NicolaCourtier]

Thanks Sarah!

[codecov]

Codecov Report

✅ All modified and coverable lines are covered by tests.
✅ Project coverage is 92.90%. Comparing base (3171a07) to head (5042a0c).
⚠️ Report is 17 commits behind head on develop.

Additional details and impacted files

@@             Coverage Diff             @@
##           develop     #982      +/-   ##
===========================================
+ Coverage    92.13%   92.90%   +0.76%     
===========================================
  Files           74       84      +10     
  Lines         5799     6777     +978     
===========================================
+ Hits          5343     6296     +953     
- Misses         456      481      +25     

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