Add Psalm files to .gitattributes

- Related to #27

[ci skip]

Signed-off-by: Maurício Meneghini Fauth <mauricio@fauth.dev>

Author: MauricioFauth

.gitattributes

@@ -7,4 +7,6 @@ codecov.yml export-ignore
 phpcs.xml.dist export-ignore
 phpstan-baseline.neon export-ignore
 phpstan.neon.dist export-ignore
+psalm.xml export-ignore
+psalm-baseline.xml export-ignore
 CODE_OF_CONDUCT.md export-ignore