krane-bundle: clarify error message when go not in PATH

[cbgbt]

Description of changes:
When go isn't in PATH, krane-bundle fails to build with a pretty opaque error message:

  --- stderr
  + UPSTREAM_SOURCE_FALLBACK=''\''false'\'''
  ++ awk -F '[ ()]' '/^SHA512 \(/ {
          printf "https://cache.bottlerocket.aws/%s/%s/%s\n", $3, $6, $3
      }' /home/ec2-user/twoliter/tools/krane/hashes/crane
  + curl --fail --remote-name-all --remote-time https://cache.bottlerocket.aws/go-containerregistry-v0.20.1.tar.gz/c323c5b78c35fb7af67641fa4ef1802b944f8bd908163ff40a952a0c190e2dd210100efba1fbc2064495cff28a60d5bc7ee98e510ec116522c7897539b02fad8/go-containerregistry-v0.20.1.tar.gz
    % Total    % Received % Xferd  Average Speed   Time    Time     Time  Current
                                   Dload  Upload   Total   Spent    Left  Speed
100 4316k  100 4316k    0     0  25.0M      0 --:--:-- --:--:-- --:--:-- 25.0M
  + sha512sum --check /home/ec2-user/twoliter/tools/krane/hashes/crane
  thread 'main' panicked at tools/krane/build.rs:81:10:
  Failed to build crane: Os { code: 2, kind: NotFound, message: "No such file or directory" }
  note: run with `RUST_BACKTRACE=1` environment variable to display a backtrace

Testing done:
When golang is missing, the error now looks like this:

error: failed to run custom build command for `krane-bundle v0.1.0 (/home/ec2-user/twoliter/tools/krane)`

Caused by:
  process didn't exit successfully: `/home/ec2-user/twoliter/target/debug/build/krane-bundle-8e3d7c3fa1de60cc/build-script-build` (exit status: 101)
  --- stdout
  cargo::rerun-if-changed=../build-cache-fetch
  cargo::rerun-if-changed=hashes/crane
  cargo::rerun-if-changed=patches

  --- stderr
  thread 'main' panicked at tools/krane/build.rs:87:14:
  Must have the `go` utility installed in PATH: CannotFindBinaryPath
  note: run with `RUST_BACKTRACE=1` environment variable to display a backtrace

Terms of contribution:

By submitting this pull request, I agree that this contribution is dual-licensed under the terms of both the Apache License, version 2.0, and the MIT license.

[koooosh]

The CI build is failing with:

error: use of `expect` followed by a function call
  --> tools/krane/build.rs:87:14
   |
87 |             .expect(format!("Must have the `{tool}` utility installed in PATH").as_str());
   |              ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^ help: try: `unwrap_or_else(|_| panic!("Must have the `{tool}` utility installed in PATH"))`

[cbgbt]

@koooosh thanks! I should have run clippy locally.