Fix plot_utilities.py

[adtzlr]

• Catch return values of plot functions.
• Remove unused increments argument in history plot.

fixes #48

[codecov[bot]]

Codecov Report

Patch coverage: 100.00% and no project coverage change.

Comparison is base (1ab8b77) 89.63% compared to head (ab20a40) 89.63%.

Additional details and impacted files

```diff @@ Coverage Diff @@ ## main #49 +/- ## ======================================= Coverage 89.63% 89.63% ======================================= Files 27 27 Lines 1244 1244 ======================================= Hits 1115 1115 Misses 129 129 ``` | [Impacted Files](https://app.codecov.io/gh/adtzlr/trusspy/pull/49?src=pr&el=tree&utm_medium=referral&utm_source=github&utm_content=comment&utm_campaign=pr+comments&utm_term=Andreas+Dutzler) | Coverage Δ | | |---|---|---| | [src/trusspy/model.py](https://app.codecov.io/gh/adtzlr/trusspy/pull/49?src=pr&el=tree&utm_medium=referral&utm_source=github&utm_content=comment&utm_campaign=pr+comments&utm_term=Andreas+Dutzler#diff-c3JjL3RydXNzcHkvbW9kZWwucHk=) | `97.58% <100.00%> (ø)` | | | [src/trusspy/tools/plot\_utilities.py](https://app.codecov.io/gh/adtzlr/trusspy/pull/49?src=pr&el=tree&utm_medium=referral&utm_source=github&utm_content=comment&utm_campaign=pr+comments&utm_term=Andreas+Dutzler#diff-c3JjL3RydXNzcHkvdG9vbHMvcGxvdF91dGlsaXRpZXMucHk=) | `77.55% <100.00%> (ø)` | |

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