[mlir][tensor] Fix bug in insert_slice canonical. with tensor encoding (#81045)

Previously, `InsertSliceOpSourceCastInserter` was incorrectly applied to
a case when tensor types have an encoding attribute attached to them.
The type `newSrcType` was missing that attribute from the old `srcType`,
which made the expression `srcType == newSrcType` false, since
`tensor<2x2xf32, "foo">` is not equal to `tensor<2x2xf32>`. That lead to
an endless back and forth between `InsertSliceOpSourceCastInserter` that
would introduce a cast and `InsertSliceOpCastFolder` that would remove
it right after.