mise upgrade removes platform entries in lock file

[muzimuzhi]

mise upgrade removes all mise.lock platform entries except for the current platform.

A reproduction example:

$ mise --version
2026.2.11 macos-x64 (2026-02-12)

# use an outdated actionlint, create lockfile which contains 5 platform entries
$ mise use actionlint@1.7.10
$ mise lock
→ Targeting 5 platform(s) for /path/to/mise.lock: linux-arm64, linux-x64, macos-arm64, macos-x64, windows-x64
→ Processing 1 tool(s): actionlint@1.7.10
lock                      actionlint@1.7.10 windows-x64                                ✔
✓ Updated 5 platform entries (0 skipped)

# make the actionlint outdated. after upgrading, lockfile contains only the entry for current platform
$ echo "[tools]\nactionlint = \"latest\"" > mise.toml
$ mise upgrade
$ cat mise.lock
[[tools.actionlint]]
version = "1.7.10"
backend = "aqua:rhysd/actionlint"
"platforms.macos-x64" = { checksum = "sha256:16782c41f2af264db80f855ee5d09164ca98fc78edf3bcd0f46eecff279682ba", url = "https://github.com/rhysd/actionlint/releases/download/v1.7.10/actionlint_1.7.10_darwin_amd64.tar.gz"}