tokio: bump parking_lot to 0.12.5

[ADD-SP]

See #7653.

We cannot revert 0248697 because of the same issue of socket2 (rust-lang/socket2#616).

error[E0557]: feature has been removed
  --> /home/dev/.cargo/registry/src/index.crates.io-1949cf8c6b5b557f/socket2-0.6.0/src/lib.rs:57:29
   |
57 | #![cfg_attr(docsrs, feature(doc_auto_cfg))]
   |                             ^^^^^^^^^^^^ feature has been removed
   |
   = note: removed in CURRENT_RUSTC_VERSION; see <https://github.com/rust-lang/rust/pull/138907> for more information
   = note: merged into `doc_cfg`

[Darksonn]

Is the bump actually needed? I don't think we run with old dependencies when building docs.

[ADD-SP]

Is the bump actually needed? I don't think we run with old dependencies when building docs.

Ah, you are right.