add GRASS8 to build tests

[t0b3]

add GRASS8 to build tests

this PR adds GRASS8 to build tests

• it serves to systematically detect compatibility issues between qgis and grass
  • i.e. build errors like libgrass_imagery: missing SONAME OSGeo/grass#2268 or fix: compile with qt6 and grass #47850 could be auto detected with such a test.

[github-actions]

The QGIS project highly values your contribution and would love to see this work merged! Unfortunately this PR has not had any activity in the last 14 days and is being automatically marked as "stale". If you think this pull request should be merged, please check

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  • link to any issues which this pull request fixes

  • add a description of workflows which this pull request fixes

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[nyalldawson]

@t0b3 can you temporarily touch a file in src/core so that the full set of workflows is run?

[t0b3]

@nyalldawson you mean these workflows here?

AFAICT they are not available anymore thus they won't run - however they were expected until now in this workflow and therefore listed here.
OTOH other workflows are new and haven't been required until now, however they will be required once merged...

Just tell me whatever I shall do, I will for sure assist and certainly could touch or change whatever you think would be helpful.