change format of hours_to_expiration for materialized view

[karlohrn]

to instead of using timestamp use a sql string.

Resolve #1173

Problem

Incorrect format of string missing "" around timestamp

Solution

change format to similare format solution used in impl.py
expiration = f'TIMESTAMP_ADD(CURRENT_TIMESTAMP(), INTERVAL {config.get("hours_to_expiration")} hour)'

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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