Update tracking issue for const_binary_heap_new_in

[Coekjan]

This PR updates the tracking issue of const_binary_heap_new_in feature:

• Old issue: Constification of BinaryHeap construction #112353
• New issue: Tracking Issue for const_binary_heap_new_in #125961

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[oli-obk]

Ah I assumed it was just going to be paired with #32838 when stabilizing the new_in method

[Coekjan]

Ah I assumed it was just going to be paired with #32838 when stabilizing the new_in method

Thank you for your feedback!

I believe the const_binary_heap_new_in feature has a different feature gate from #32838 (allocator_api). Therefore, it should be stabilized separately after #32838 is stabilized. However, if it's feasible to merge it into the allocator_api feature, that might be a better approach.

[joboet]

For me, merging into allocator_api makes sense, but let's see what someone from the API team has to say.
r? libs-api