v2.1.0 changelog

• Fix #147: Make timestamps in generated report more accurate.
• Fix #140: Escape illegal XML characters in junit output.
• Fix #145: Handle build errors in test packages with the _test suffix.
• Fix #145: Don't ignore build errors that did not belong to a package.
• Fix #134: Json test output was not parsed correctly when using the -race flag in go test.
• Add support for === NAME lines introduced in Go1.20
• junit: Add File attribute to testsuite.
• junit: Allow multiple properties with the same name.
• junit: Add the Testsuites.WriteXML convenience method.