Update SparkHook configuration loading line on docs.

[lrcouto]

Description

#4118 and #4166 pointed out that the way our documentation instructs users to load the spark.yml config file might be incorrect. The changed line should work, assuming that the file is at conf/base/spark.yml.

Development notes

Developer Certificate of Origin

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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]

LGTM but I don't have time to QA this at the moment, consider requesting reviews from the rest of the team!