Use attribute to implement these conversions

[jfly]

pr-tracker/crates/api/src/lib.rs

Lines 80 to 90 in 4b7a09e

	impl From<PrNumberNonPositiveError> for LandedError {
	fn from(value: PrNumberNonPositiveError) -> Self {
	Self::PrNumberNonPositive(value)
	}
	}
	impl From<ForPrError> for LandedError {
	fn from(value: ForPrError) -> Self {
	Self::ForPr(value)
	}
	}