Update steel diffusion constraints

[GamzeUnlu95]

Update steel diffusion constraints as follows:

• removed growth_activity_lo and initial_activity_lo for bof_steel from 2030 onwards
• changed the growth_activity_up for dri_gas_steel, dri_h2_steel, and eaf_steel to 0.075 from 2030 onwards
• changed the initial_activity_up for dri_gas_steel and dri_h2_steel to 1.0 from 2030 onwards

How to review

No review is needed, just changing the parameters in Excel data file as agreed before.

PR checklist

• [x] Continuous integration checks all ✅

[codecov[bot]]

Codecov Report

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

Project coverage is 75.5%. Comparing base (6032244) to head (e4e8eaf). Report is 1 commits behind head on main.

Additional details and impacted files

```diff @@ Coverage Diff @@ ## main #247 +/- ## ======================================= - Coverage 76.5% 75.5% -1.0% ======================================= Files 203 203 Lines 15546 15546 ======================================= - Hits 11896 11748 -148 - Misses 3650 3798 +148 ``` [see 7 files with indirect coverage changes](https://app.codecov.io/gh/iiasa/message-ix-models/pull/247/indirect-changes?src=pr&el=tree-more&utm_medium=referral&utm_source=github&utm_content=comment&utm_campaign=pr+comments&utm_term=iiasa)