chore: removed java-spanner from required downstream check (#424)

This changes will be reverted after [this](googleapis/java-spanner#1329) PR gets merged in. Github actions in java-spanner repo is preventing the PR from being merged.

.github/sync-repo-settings.yaml

@@ -17,11 +17,9 @@ branchProtectionRules:
       - units (11)
       - 'Kokoro - Test: Integration'
       - dependencies (8, java-bigqueryconnection)
-      - dependencies (8, java-spanner)
       - dependencies (8, java-storage)
       - dependencies (8, java-pubsub)
       - dependencies (11, java-bigqueryconnection)
-      - dependencies (11, java-spanner)
       - dependencies (11, java-storage)
       - dependencies (11, java-pubsub)
       - cla/google