Do not export MAINTAINERS.md and psalm.xml

Author: williamdes

.gitattributes

@@ -10,9 +10,11 @@
 /.gitignore         export-ignore
 /CODE_OF_CONDUCT.md export-ignore
 /CONTRIBUTING.md    export-ignore
+/MAINTAINERS.md     export-ignore
 /README.md          export-ignore
 /UPGRADING.md       export-ignore
 /phpcs.xml.dist     export-ignore
 /phpstan.neon.dist  export-ignore
 /phpunit.xml.dist   export-ignore
+/psalm.xml          export-ignore
 /tests              export-ignore