Don't repeat the Oracle password in ci/build.yml (#9419)

Got it from https://stackoverflow.com/a/13802438

Incidentally, to write this commit message containing a single quote, I had to escape it with this https://stackoverflow.com/a/1250279

I guess today is "bring-your-quotation-marks-to-work day".

changelog_begin
changelog_end

ci/build.yml

@@ -230,7 +230,7 @@ jobs:
         }
         trap cleanup EXIT
         testConnection() {
-            docker exec oracle bash -c 'sqlplus -L system/hunter2@//localhost:1521/ORCLPDB1 <<< "select * from dba_users;"; exit $?' >/dev/null
+            docker exec oracle bash -c 'sqlplus -L system/'"$ORACLE_PWD"'@//localhost:1521/ORCLPDB1 <<< "select * from dba_users;"; exit $?' >/dev/null
         }
         until testConnection
         do