Switch ceil to floor

[dapollak]

resolves #
docs dbt-labs/docs.getdbt.com/#

Problem

When calculating datediff in "hour"s with spark, we get a result that is larger by 1 relatively to all other warehouses when using datediff.

Solution

Swapping CEIL and FLOOR as in all other cases

Checklist

• I have read the contributing guide and understand what's expected of me
• I have run this code in development and it appears to resolve the stated issue
• This PR includes tests, or tests are not required/relevant for this PR
• This PR has no interface changes (e.g. macros, cli, logs, json artifacts, config files, adapter interface, etc) or this PR has already received feedback and approval from Product or DX

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