Use appropriate default value for sketches-reports-source input

[per1234]

In the time since it was first conceived, the use of the report file created by the arduino/compile-sketches action has been expanded from only being a way to pass memory usage change data to the arduino/report-size-deltas action to a general purpose report of data generated from the sketch compilations, including:

• Non-deltas size data consumed by arduino/report-size-trends
• Compilation status for each sketch/board combination
• Compiler warning count

It's possible additional information will be added to the report over time.

For this reason, the previous default of the arduino/compile-sketches action's sketches-report-path input: size-deltas-reports was no longer appropriate and had to be changed to avoid confusion. Even though arduino/report-size-deltas only uses the deltas data from the report, and so the previous default was somewhat logical, I think it's best for the same default name to be used for the folder and workflow artifacts containing the reports consistently across all the actions that use this report.

Unfortunately, this will be a breaking change for people who have not specified the action's sketches-reports-source input in their workflow and are thus relying on the default value.

[aentinger]

Although a breaking change those are sometimes necessary. As we are currently our own best action customer I agree on doing this breaking change now before the actions get widespread usage. Good work @per1234 🚀