Use 'os' instead of 'ioutil' in gazelle tests - #962

PR Checklist

Please check if your PR fulfills the following requirements:

• Tests for the changes have been added (for bug fixes / features)
• Docs have been added / updated (for bug fixes / features)

PR Type

What kind of change does this PR introduce?

• Bugfix
• Feature (please, look at the "Scope of the project" section in the README.md file)
• Code style update (formatting, local variables)
• Refactoring (no functional changes, no api changes)
• Build related changes
• CI related changes
• Documentation content changes
• Other... Please describe:

What is the current behavior?

We are currently using ioutil.ReadFile in gazelle tests even though it has been deprecated since 1.16 as per official docs.

What is the new behavior?

Use os.ReadFile instead as the package suggests.

Does this PR introduce a breaking change?

• Yes
• No

Other information