check usage of `.spec()` and `.specs()` in codebase

[kevinjqliu]

Apache Iceberg version

None

Please describe the bug 🐞

Context: https://github.com/apache/iceberg-python/pull/2293/files#r2258601170

Make sure we use the correctly PartitionSpec. .spec() implicitly returns the current partition spec of the table

Willingness to contribute

• I can contribute a fix for this bug independently
• I would be willing to contribute a fix for this bug with guidance from the Iceberg community
• I cannot contribute a fix for this bug at this time