bazelisk has different PATH for workspace_status_command

My team's bazel setup involves invoking a script for `--workspace_status_command` (this flag is defined in our bazelrc).

The script in question invokes `dirname`, which is a common utility under `/usr/bin`.

This operates correctly using Bazel, because the `PATH` in the environment for our Bazel invocation includes `/usr/bin`.
When using `bazelisk`, this script fails because the env value of `PATH` in this invocation is only `~/.cache/bazelisk/downloads/bazelbuild/bazel-${commithash}-linux-x86_64/bin`, which does not contain `dirname`.

No source file or test is named. Start by tracing how Bazelisk constructs the environment for the Bazel invocation and how it handles --workspace_status_command; compare that PATH with a direct Bazel invocation. Done means the workspace status script can resolve dirname and other standard utilities when run through Bazelisk, with a regression test covering the environment.

Written by the indexing model from the issue text.