fix: Return non-zero exit code on lint failures

[mildaniel]

Which issue(s) does this change fix?

#4649

Why is this change necessary?

Currently, sam validate --lint returns a 0 return code even if lint errors occurred.

How does it address the issue?

Raises an exception if any lint rules matched, which will propagate up and will exit the process with a return code of 1.

What side effects does this change have?

N/A

Mandatory Checklist

PRs will only be reviewed after checklist is complete

• Add input/output type hints to new functions/methods
• Write design document if needed (Do I need to write a design document?)
• Write/update unit tests
• Write/update integration tests
• Write/update functional tests if needed
• make pr passes
• make update-reproducible-reqs if dependencies were changed
• Write documentation

By submitting this pull request, I confirm that my contribution is made under the terms of the Apache 2.0 license.

[sriram-mv]

If there are 0 matches, do we know that we are in exit code 1 state by default?

[mildaniel]

The opposite actually. Line 148 checks for any matches and logs a success message if none are found

if not matches:
     click.secho("{} is a valid SAM Template".format(template), fg="green")

Otherwise there are some rules matched (meaning the linter found some issues) and we're in exit code 1 state.