Handle uninitialized variable in `propagate_solution` of scaling transformation

[Robbybp]

Fixes #3273

Changes proposed in this PR:

• If a variable has a value of None in the scaled model, we don't attempt to set its value in the original model

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[codecov[bot]]

Codecov Report

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

Project coverage is 88.56%. Comparing base (6fb0c5d) to head (dc04352). Report is 97 commits behind head on main.

Additional details and impacted files

```diff @@ Coverage Diff @@ ## main #3275 +/- ## ========================================== + Coverage 88.51% 88.56% +0.04% ========================================== Files 865 865 Lines 97585 97586 +1 ========================================== + Hits 86381 86427 +46 + Misses 11204 11159 -45 ``` | [Flag](https://app.codecov.io/gh/Pyomo/pyomo/pull/3275/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/3275/flags?src=pr&el=flag&utm_medium=referral&utm_source=github&utm_content=comment&utm_campaign=pr+comments&utm_term=Pyomo) | `86.49% <100.00%> (+<0.01%)` | :arrow_up: | | [osx](https://app.codecov.io/gh/Pyomo/pyomo/pull/3275/flags?src=pr&el=flag&utm_medium=referral&utm_source=github&utm_content=comment&utm_campaign=pr+comments&utm_term=Pyomo) | `75.84% <100.00%> (+<0.01%)` | :arrow_up: | | [other](https://app.codecov.io/gh/Pyomo/pyomo/pull/3275/flags?src=pr&el=flag&utm_medium=referral&utm_source=github&utm_content=comment&utm_campaign=pr+comments&utm_term=Pyomo) | `86.68% <100.00%> (+<0.01%)` | :arrow_up: | | [win](https://app.codecov.io/gh/Pyomo/pyomo/pull/3275/flags?src=pr&el=flag&utm_medium=referral&utm_source=github&utm_content=comment&utm_campaign=pr+comments&utm_term=Pyomo) | `83.97% <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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[Robbybp]

This should fix #2817 as well.