Tests for grafting of file data sources

[leoyvens]

The entity copy query used by grafting has special cases for each combination of source and target has_causality_region value:

graph-node/store/postgres/src/relational_queries.rs

Lines 3583 to 3599 in 7118fd8

	match (self.src.has_causality_region, self.dst.has_causality_region) {
	(false, false) => (),
	(true, true) => {
	out.push_sql(", ");
	out.push_sql(CAUSALITY_REGION_COLUMN);
	}
	(false, true) => {
	out.push_sql(", 0");
	}
	(true, false) => {
	return Err(constraint_violation!(
	"can not copy entity type {} to {} because the src has a causality region but the dst does not",
	self.src.object.as_str(),
	self.dst.object.as_str()
	));
	}
	}

Except for the noop (false, false), these are not currently covered by our tests.

[github-actions]

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