`fit_background` fixes

[ericpre]

Fitting the background in EDS model doesn't work with linear fitting, because the twin lines are disactivated properly when running linear fitting.

import exspy

s = exspy.data.EDS_SEM_TM002()
m = s.isig[5.0:15.0].create_model()
m.plot()
m.fit_background(optimizer="lstsq")

which will raise the following error:

    m.fit_background(optimizer="lstsq")

  File ~\Dev\exspy\exspy\models\edsmodel.py:394 in fit_background
    self.fit(**kwargs)

  File ~\Dev\hyperspy\hyperspy\model.py:1797 in fit
    fit_output = self._linear_fit(

  File ~\Dev\hyperspy\hyperspy\model.py:1217 in _linear_fit
    index = parameters.index(p)

ValueError: <Parameter A of Cu_Ka component> is not in list

Progress of the PR

• [x] Fix fit_background with linear fitting,
• [x] fix resetting signal range after fitting background,
• [x] suspend plot when fitting background,
• [x] simplify/shorten title of EDS maps,
• [n/a] docstring updated (if appropriate),
• [n/a] update user guide (if appropriate),
• [x] added tests,
• [x] add a changelog entry in the upcoming_changes folder (see upcoming_changes/README.rst),
• [x] Check formatting of the changelog entry (and eventual user guide changes) in the docs/readthedocs.org:exspy build of this PR (link in github checks)
• [x] ready for review.

[codecov[bot]]

Codecov Report

Attention: Patch coverage is 93.75000% with 3 lines in your changes missing coverage. Please review.

Project coverage is 88.69%. Comparing base (75ca046) to head (88949ab). Report is 9 commits behind head on main.

Files with missing lines	Patch %	Lines
exspy/models/edsmodel.py	86.95%	1 Missing and 2 partials :warning:

Additional details and impacted files

```diff @@ Coverage Diff @@ ## main #76 +/- ## ========================================== + Coverage 88.62% 88.69% +0.06% ========================================== Files 76 76 Lines 7411 7439 +28 Branches 1192 1197 +5 ========================================== + Hits 6568 6598 +30 + Misses 574 572 -2 Partials 269 269 ```

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