Add support for postgres version 15 (#4)

Author: tbay06

install-pg-dump.sh

@@ -8,8 +8,8 @@ if [[ -z "$POSTGRES_VERSION" ]]; then
   exit 1
 fi
 
-if [[ "$POSTGRES_VERSION" != @(11|12|13|14) ]]; then
-  echo "POSTGRES_VERSION must be one of 11, 12, 13, 14"
+if [[ "$POSTGRES_VERSION" != @(11|12|13|14|15) ]]; then
+  echo "POSTGRES_VERSION must be one of 11, 12, 13, 14, 15"
   exit 1
 fi