exclude tests/ from releases (#288)

Author: staabm

.gitattributes

@@ -1,4 +1,10 @@
+# mark cache files as generated files, so they don't show up in Pull Requests diffs
 .phpstan-dba-mysqli.cache linguist-generated=true
 .phpstan-dba-pdo.cache linguist-generated=true
 .phpunit-phpstan-dba-mysqli.cache linguist-generated=true
 .phpunit-phpstan-dba-pdo.cache linguist-generated=true
+
+# Exclude non-essential files from dist
+/tests export-ignore
+.phpunit-phpstan-dba-mysqli.cache
+.phpunit-phpstan-dba-pdo.cache