update .gitattributes to exclude additional directories from export

Author: koriym

.gitattributes

@@ -13,6 +13,10 @@
 /phpunit.xml.dist export-ignore
 /psalm.xml        export-ignore
 /composer-require-checker.json  export-ignore
+/.claude          export-ignore
+/doc              export-ignore
+/demo             export-ignore
+/.github          export-ignore
 
 # Configure diff output for .php and .phar files.
 *.php diff=php