Set a consistent file name in testing docs

[lvvittor]

Description

Normalize the testing file name in the documentation and remove extra indentation in Python code blocks.

Development notes

The documentation for adding test is not well written, for this PR I normalize the file names and remove extra indentation in the examples.

Developer Certificate of Origin

We need all contributions to comply with the Developer Certificate of Origin (DCO). All commits must be signed off by including a Signed-off-by line in the commit message. See our wiki for guidance.

If your PR is blocked due to unsigned commits, then you must follow the instructions under "Rebase the branch" on the GitHub Checks page for your PR. This will retroactively add the sign-off to all unsigned commits and allow the DCO check to pass.

Checklist

• Read the contributing guidelines
• Signed off each commit with a Developer Certificate of Origin (DCO)
• Opened this PR as a 'Draft Pull Request' if it is work-in-progress
• Updated the documentation to reflect the code changes
• Added a description of this change in the RELEASE.md file
• Added tests to cover my changes
• Checked if this change will affect Kedro-Viz, and if so, communicated that with the Viz team

[astrojuanlu]

Thanks a lot @lvvittor! 🙌🏼

[lvvittor]

@yetudada could you approve this PR so I can write the release file and merge the PR?

[imMatheus]

Wow, this is the best PR ever man! I just got some issues with this, thanks for fixing @lvvittor!

[astrojuanlu]

Requested another review from the team 🙏🏼

[ankatiyar]

Thanks @lvvittor 💯