Change the way `go fmt` is executed

[gchappel]

Since $@ contains a filtered list of all *.go files that are staged for the commit, calling go fmt on them individually stops the error being thrown when trying to run go fmt against a subdirectory, from a directory which does not contain a go.mod file

Description

This is one potential workaround for the issue described by me in issue #67

Documentation

TODOs

Please ensure all of these TODOs are completed before asking for a review.

• [x] Ensure the branch is named correctly with the issue number. e.g: feature/new-vpc-endpoints-955 or bug/missing-count-param-434.
• [n/a] Update the docs.
• [x] Keep the changes backward compatible where possible.
• [x] Run the pre-commit checks successfully.
• [n/a] Run the relevant tests successfully.

Related Issues

Fixes #67