build: bump once_cell from 1.12.0 to 1.12.1

Bumps [once_cell](https://github.com/matklad/once_cell) from 1.12.0 to 1.12.1.
- [Release notes](https://github.com/matklad/once_cell/releases)
- [Changelog](https://github.com/matklad/once_cell/blob/master/CHANGELOG.md)
- [Commits](https://github.com/matklad/once_cell/compare/v1.12.0...v1.12.1)

---
updated-dependencies:
- dependency-name: once_cell
  dependency-type: direct:production
  update-type: version-update:semver-patch
...

Signed-off-by: dependabot[bot] <support@github.com>

test_infra/Cargo.toml

@@ -8,7 +8,7 @@ edition = "2021"
 dirs = "4.0.0"
 epoll = "4.3.1"
 libc = "0.2.126"
-once_cell = "1.12.0"
+once_cell = "1.12.1"
 ssh2 = { version = "0.9.1", features = ["vendored-openssl"]}
 vmm-sys-util = "0.9.0"
 wait-timeout = "0.2.0"