Fix LoaderHeap's free list growing more than expected (#129203)

This PR stops making thread race to create/publish such that we don't insert several blocks in the free list.

| | .NET 10 | .NET 10 + this PR |
|---|---|---|
| Time | 91.2 s | 3.9 s |
| Max RSS | 114.1 MB | 117.5 MB |

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Co-authored-by: Ubuntu <azure@eduardo-linux.sql0fxglchme5jhu4spsf5nbmb.xx.internal.cloudapp.net>
Co-authored-by: Eduardo Velarde <evelardepola@microsoft.com>
Co-authored-by: Copilot Autofix powered by AI <175728472+Copilot@users.noreply.github.com>

Author: 4 people