Rollup merge of rust-lang#123378 - ferrocene:hoverbear/bump-sysinfo-to-0.30.8, r=Nilstrieb

Update sysinfo to 0.30.8

Fixes a Mac specific issue when using `metrics = true` in `config.toml`.

```config.toml
# Collect information and statistics about the current build and writes it to
# disk. Enabling this or not has no impact on the resulting build output. The
# schema of the file generated by the build metrics feature is unstable, and
# this is not intended to be used during local development.
metrics = true
```

During repeated builds, as the generated `metrics.json` grew, eventually `refresh_cpu()` would be called in quick enough succession (specifically: under 200ms) that a divide by zero would occur, leading to a `NaN` which would not be serialized, then when the `metrics.json` was re-read it would fail to parse.

That error looks like this (collected from Ferrocene's CI):

```
   Compiling rustdoc-tool v0.0.0 (/Users/distiller/project/src/tools/rustdoc)
    Finished release [optimized] target(s) in 38.37s
thread 'main' panicked at src/utils/metrics.rs:180:21:
serde_json::from_slice::<JsonRoot>(&contents) failed with invalid type: null, expected f64 at line 1 column 9598
note: run with `RUST_BACKTRACE=1` environment variable to display a backtrace
Build completed unsuccessfully in 0:00:40

Exited with code exit status 1
```

Related: GuillaumeGomez/sysinfo#1236

Author: matthiaskrgr

Cargo.lock

@@ -5370,9 +5370,9 @@ dependencies = [
 
 [[package]]
 name = "sysinfo"
-version = "0.30.7"
+version = "0.30.8"
 source = "registry+https://github.com/rust-lang/crates.io-index"
-checksum = "0c385888ef380a852a16209afc8cfad22795dd8873d69c9a14d2e2088f118d18"
+checksum = "4b1a378e48fb3ce3a5cf04359c456c9c98ff689bcf1c1bc6e6a31f247686f275"
 dependencies = [
  "cfg-if",
  "core-foundation-sys",