Raise error in `generate_strongly_connected_components` instead of asserting

[Robbybp]

Fixes #3297

More useful error message.

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[codecov[bot]]

Codecov Report

All modified and coverable lines are covered by tests :white_check_mark:

Project coverage is 88.49%. Comparing base (f5e6f32) to head (fe79414). Report is 22 commits behind head on main.

Additional details and impacted files

```diff @@ Coverage Diff @@ ## main #3305 +/- ## ========================================== - Coverage 88.50% 88.49% -0.01% ========================================== Files 868 868 Lines 98427 98430 +3 ========================================== - Hits 87112 87107 -5 - Misses 11315 11323 +8 ``` | [Flag](https://app.codecov.io/gh/Pyomo/pyomo/pull/3305/flags?src=pr&el=flags&utm_medium=referral&utm_source=github&utm_content=comment&utm_campaign=pr+comments&utm_term=Pyomo) | Coverage Δ | | |---|---|---| | [linux](https://app.codecov.io/gh/Pyomo/pyomo/pull/3305/flags?src=pr&el=flag&utm_medium=referral&utm_source=github&utm_content=comment&utm_campaign=pr+comments&utm_term=Pyomo) | `86.30% <100.00%> (+<0.01%)` | :arrow_up: | | [osx](https://app.codecov.io/gh/Pyomo/pyomo/pull/3305/flags?src=pr&el=flag&utm_medium=referral&utm_source=github&utm_content=comment&utm_campaign=pr+comments&utm_term=Pyomo) | `75.61% <100.00%> (-0.01%)` | :arrow_down: | | [other](https://app.codecov.io/gh/Pyomo/pyomo/pull/3305/flags?src=pr&el=flag&utm_medium=referral&utm_source=github&utm_content=comment&utm_campaign=pr+comments&utm_term=Pyomo) | `86.50% <100.00%> (+<0.01%)` | :arrow_up: | | [win](https://app.codecov.io/gh/Pyomo/pyomo/pull/3305/flags?src=pr&el=flag&utm_medium=referral&utm_source=github&utm_content=comment&utm_campaign=pr+comments&utm_term=Pyomo) | `83.81% <100.00%> (+<0.01%)` | :arrow_up: | Flags with carried forward coverage won't be shown. [Click here](https://docs.codecov.io/docs/carryforward-flags?utm_medium=referral&utm_source=github&utm_content=comment&utm_campaign=pr+comments&utm_term=Pyomo#carryforward-flags-in-the-pull-request-comment) to find out more.

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