Tell shellcheck to follow sourced files

[mattlord]

Description

This is a minor improvement that will help eliminate unhelpful shellcheck errors — surfaced via the pre-commit hooks: .git/hooks/pre-commit -> misc/git/hooks/shellcheck — as well as potentially surface new things.

It does this by adding the -x shell flag so that shellcheck will follow the files and validate them as well. Here's an example:

❯ shellcheck tools/remove_dependencies.sh

In tools/remove_dependencies.sh line 21:
source build.env
       ^-------^ SC1091 (info): Not following: build.env was not specified as input (see shellcheck -x).

For more information:
  https://www.shellcheck.net/wiki/SC1091 -- Not following: build.env was not ...

❯ shellcheck -x tools/remove_dependencies.sh

Related Issue(s)

Checklist

• "Backport to:" labels have been added if this change should be back-ported
• Tests were added or are not required
• Did the new or modified tests pass consistently locally and on the CI
• Documentation was added or is not required

[vitess-bot]

Review Checklist

Hello reviewers! 👋 Please follow this checklist when reviewing this Pull Request.

General

• Ensure that the Pull Request has a descriptive title.
• Ensure there is a link to an issue (except for internal cleanup and flaky test fixes), new features should have an RFC that documents use cases and test cases.

Tests

• Bug fixes should have at least one unit or end-to-end test, enhancement and new features should have a sufficient number of tests.

Documentation

• Apply the release notes (needs details) label if users need to know about this change.
• New features should be documented.
• There should be some code comments as to why things are implemented the way they are.
• There should be a comment at the top of each new or modified test to explain what the test does.

New flags

• Is this flag really necessary?
• Flag names must be clear and intuitive, use dashes (-), and have a clear help text.

If a workflow is added or modified:

• Each item in Jobs should be named in order to mark it as required.
• If the workflow needs to be marked as required, the maintainer team must be notified.

Backward compatibility

• Protobuf changes should be wire-compatible.
• Changes to _vt tables and RPCs need to be backward compatible.
• RPC changes should be compatible with vitess-operator
• If a flag is removed, then it should also be removed from vitess-operator and arewefastyet, if used there.
• vtctl command output order should be stable and awk-able.