Better errors for logging corner cases

[carmocca]

What does this PR do?

Fixes #12863

Does your PR introduce any breaking changes? If yes, please list them.

Logging a non-scalar tensor now raises an error instead of computing the mean internally.

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cc @Borda @carmocca @edward-io @ananthsub @rohitgr7 @kamil-kaczmarek @Raalsky @Blaizzy

[tchaton]

LGTM !