Rust warnings in V8 CI

Seen in https://ci.nodejs.org/job/node-test-commit-v8-linux/7172/nodes=benchmark-ubuntu2404-intel-64,v8test=v8test/console

10:38:04 [3556/3806] RUST local_rustc_sysroot/lib/rustlib/x86_64-unknown-linux-gnu/lib/libobject_object.rlib local_rustc_sysroot/lib/rustlib/x86_64-unknown-linux-gnu/lib/libobject_object.rmeta obj/build/rust/std/rules/object.rustflags.json obj/build/rust/std/rules/object.rsp.rust
10:38:04 warning: failed to connect to jobserver from environment variable `MAKEFLAGS=" -j20 --jobserver-auth=3,4 --no-print-directory -- V8_EXTRA_TEST_OPTIONS=--progress=dots\\ --timeout=120\\ intl ENABLE_CONVERT_V8_JSON_TO_XML=True ARCH=x64.release DESTCPU=x64 V=1"`: cannot open file descriptor 3 from the jobserver environment variable value: Bad file descriptor (os error 9)
10:38:04   |
10:38:04   = note: the build environment is likely misconfigured
10:38:04 

Start with the linked V8 CI console output and investigate the Rust jobserver warning in the CI build environment. Done means the misconfigured jobserver warning no longer appears in the relevant V8 CI run, with the build still completing successfully.