[Bug]: JdbcIO.readRows() incompatible with AvroUtils for DECIMAL\NUMERIC(10,2)

### What happened?

1. use `JdbcIO.readRows()` for table with `DECIMAL(10,2)`
2. it reads BigDecimals fine but Schema has just DECIMAL type without scale
3. then, when I attempt to serialise these rows into Avro, I got
` AvroTypeException("Cannot encode decimal with scale 2 as scale 0 without rounding")
from org.apache.avro.Conversions.DecimalConversion.validate() `

mailing list https://lists.apache.org/thread/qxwron01myf5fzrb3d8tsh71grt5cpzk
PR fixes #27333

### Issue Priority

Priority: 3 (minor)

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