github/action: fix Debian 12 intermittent failures

github/action: fix Debian 12 intermittent failures

Parallel builds caused issues during `cargo vendor`. So do just a single
thread build.

 make[4]: Entering directory '/__w/suricata/suricata/rust'
cbindgen --config /__w/suricata/suricata/rust/cbindgen.toml \
	--quiet --output /__w/suricata/suricata/rust/dist/rust-bindings.h
CARGO_HOME="/github/home/.cargo"  /usr/bin/cargo vendor
    Blocking waiting for file lock on package cache
    Blocking waiting for file lock on package cache
ERROR: Couldn't execute `cargo metadata` with manifest "/__w/suricata/suricata/rust/Cargo.toml": Metadata(Output { status: ExitStatus(unix_wait_status(25856)), stdout: "", stderr: "    Blocking waiting for file lock on package cache\n    Blocking waiting for file lock on package cache\nerror: failed to download `adler v1.0.2`\n\nCaused by:\n  unable to get packages from source\n\nCaused by:\n  failed to parse manifest at `/github/home/.cargo/registry/src/github.com-1ecc6299db9ec823/adler-1.0.2/Cargo.toml`\n\nCaused by:\n  no targets specified in the manifest\n  either src/lib.rs, src/main.rs, a [lib] section, or [[bin]] section must be present\n" })
ERROR: Couldn't generate bindings for /__w/suricata/suricata/rust.
make[4]: *** [Makefile:597: dist/rust-bindings.h] Error 1
make[4]: *** Waiting for unfinished jobs....