Bump the release-branch prerelease counter to 10.4.0-rc.5

[ChrisonSimtian]

Bumps the release-branch prerelease counter from 10.4.0-rc.4 to 10.4.0-rc.5, so the next tag off release/v10.4 ships the two queued cherry-picks.

One-line change to version.json.

Why

On a release branch the prerelease number is a manual counter, not {height} — see branching-and-release.md → Prerelease numbers on a release branch are a manual counter. Tagging without bumping republishes an existing version, and dotnet nuget push --skip-duplicate swallows that silently, so the packages just don't update.

rc.5 is the first RC to carry:

• Cherry-pick the Fallout.Common.ProjectModel migration path onto 10.4 #590 — the Fallout.Common.ProjectModel transition shim (fixes the CS0234/CS0246 break consumers hit upgrading 10.3.x → rc.4).
• Cherry-pick the Fallout.GlobalTool package id onto 10.4 #593 — reverting the CLI package id to Fallout.GlobalTool, so GA continues the id the install base has pinned.

Verification

dotnet pack src/Fallout.Cli on this branch stamps 10.4.0-rc.5. (Locally it also carries a .g<commit> suffix and the pre-#593 plural id, both only because this topic branch isn't a public release ref and doesn't include #593 — on release/v10.4 with both cherry-picks in it stamps Fallout.GlobalTool.10.4.0-rc.5.)

Merge order

Independent of #590 and #593 — no file overlap, so all three can merge in any order. The only ordering that matters is the tag: cut v10.4.0-rc.5 only once all three are on release/v10.4, or the RC ships without the fixes it's numbered for.