Fix regression: report size delta size on PR.

[aentinger]

The necessary steps have in fact been documented here: https://github.com/arduino/report-size-deltas/blob/main/docs/FAQ.md#workflow-triggered-by-pull_request-event but I have overlooked them when I fixed the upload issue. With this PR the size deltas are - once again - reported within the PR.

[github-actions]

Memory usage change @ 4bbf688

Board	flash	%	RAM for global variables	%
arduino:samd:arduino_zero_edbg	0 - 0	0.0 - 0.0	0 - 0	0.0 - 0.0
arduino:samd:mkrzero	0 - 0	0.0 - 0.0	0 - 0	0.0 - 0.0
arduino:samd:nano_33_iot	0 - 0	0.0 - 0.0	0 - 0	0.0 - 0.0

Click for full report table

Board	examples/ASCIIDraw flash	%	examples/ASCIIDraw RAM for global variables	%
arduino:samd:arduino_zero_edbg	0	0.0	0	0.0
arduino:samd:mkrzero	0	0.0	0	0.0
arduino:samd:nano_33_iot	0	0.0	0	0.0

Click for full report CSV

Board,examples/ASCIIDraw<br>flash,%,examples/ASCIIDraw<br>RAM for global variables,%
arduino:samd:arduino_zero_edbg,0,0.0,0,0.0
arduino:samd:mkrzero,0,0.0,0,0.0
arduino:samd:nano_33_iot,0,0.0,0,0.0