Build/Test Tools: Pin specific Importer version.

This pins the last version compatible with WordPress 5.1 to that branch.

Follow up to [59615].
Reviewed by swissspidy.

See #52909.
See #62280.

git-svn-id: https://develop.svn.wordpress.org/branches/5.1@59629 602fd350-edb4-49c9-b593-d223f7449a82

Author: desrosj

tools/local-env/scripts/install.js

@@ -55,5 +55,5 @@ function install_wp_importer() {
 	const testPluginDirectory = 'tests/phpunit/data/plugins/wordpress-importer';
 
 	execSync( `docker compose exec -T php rm -rf ${testPluginDirectory}`, { stdio: 'inherit' } );
-	execSync( `docker compose exec -T php git clone https://github.com/WordPress/wordpress-importer.git ${testPluginDirectory} --depth=1`, { stdio: 'inherit' } );
+	execSync( `docker compose exec -T php git clone https://github.com/WordPress/wordpress-importer.git ${testPluginDirectory} --depth=1 --branch 0.7`, { stdio: 'inherit' } );
 }