Format Scala files in codesig test cases

[lefou]

Newer versions of Mill better find these nested modules (#3270), so that our CI check for formatted Scala files will fail once we bump to Mill 0.11.10 or newer.

[lihaoyi]

The tests are failing because the test framework scrapes the /* */ comment to find the expected assertion data. Should be easy to tweak the scraping (Should be

mill/main/codesig/test/src/CallGraphTests.scala

Lines 175 to 183 in a16c97d

	val openTagLine = s"/* $tag"
	sourceLinesOpt.flatMap { sourceLines =>
	sourceLines.count(_ == openTagLine) match {
	case 0 => None
	case 1 =>
	val expectedLines = sourceLines
	.dropWhile(_ != openTagLine)
	.drop(1)
	.takeWhile(_ != "*/")

) to accomadate the adjusted format.