[FLINK-31566] Updates .github/workflows/snapshot.yml to point to make all supported versions point to the right dev-* branches

1.15 is left in there for now because we might want to release 1.15.5
diff --git a/.github/workflows/snapshot.yml b/.github/workflows/snapshot.yml
index cdda9a0..b4c9511 100644
--- a/.github/workflows/snapshot.yml
+++ b/.github/workflows/snapshot.yml
@@ -38,8 +38,10 @@
       matrix:
         java_version: [8, 11]
         build:
-          - flink_version: 1.17-SNAPSHOT
+          - flink_version: 1.18-SNAPSHOT
             branch: dev-master
+          - flink_version: 1.17-SNAPSHOT
+            branch: dev-1.17
           - flink_version: 1.16-SNAPSHOT
             branch: dev-1.16
           - flink_version: 1.15-SNAPSHOT