Change to sh regex

entrypoint.sh

@@ -41,8 +41,7 @@ if [ -n "$INPUT_PRETTIER_PLUGINS" ]; then
     for plugin in $INPUT_PRETTIER_PLUGINS; do
         echo "checking $plugin"
         # check regex against @prettier/xyz
-        REGEX='(@prettier\/)+(plugin-[a-z\-]+)'
-        if ! [[ "$plugin" =~ "$REGEX" ]]; then
+        if ! echo "$plugin" | grep -Eq '(@prettier\/)+(plugin-[a-z\-]+)'; then
             echo "$plugin does not seem to be a valid @prettier/plugin-x plugin."
             exit 1
         fi