Fix failing async test

C++ integration test fails like for example here with this error:

1: Test command: /caosdb-cppinttest/build/bin/test_async "--gtest_filter=test_async.retrieve_non_existing" "--gtest_also_run_disabled_tests"
1: Test timeout computed to be: 10000000
1: Running main() from /home/conan/w/prod/BuildSingleReference/.conan/data/gtest/1.11.0/_/_/build/e019a06362b932ca5d1b082b6c112aa150c88de4/src/googletest/src/gtest_main.cc
1: Note: Google Test filter = test_async.retrieve_non_existing
1: [==========] Running 1 test from 1 test suite.
1: [----------] Global test environment set-up.
1: [----------] 1 test from test_async
1: [ RUN      ] test_async.retrieve_non_existing
1: /caosdb-cppinttest/test/test_async.cpp:61: Failure
1: Expected equality of these values:
1:   status.GetCode()
1:     Which is: -1
1:   TransactionStatus::TRANSACTION_ERROR().GetCode()
1:     Which is: 22
1: /caosdb-cppinttest/test/test_async.cpp:62: Failure
1: Expected equality of these values:
1:   status.GetCode()
1:     Which is: -1
1:   StatusCode::GENERIC_TRANSACTION_ERROR
1:     Which is: 22
1: [2023-09-25 10:36:18.287618][600] caosdb::transaction - UnaryRpcHandler finished with an error (Code 
1: [2023-09-25 10:36:18.287721][600] caosdb::transaction - 1
1: [2023-09-25 10:36:18.287747][600] caosdb::transaction - ): 
1: [2023-09-25 10:36:18.287801][600] caosdb::transaction - The operation was canceled (typically by the caller). Original message: CANCELLED
1: [  FAILED  ] test_async.retrieve_non_existing (1005 ms)
1: [----------] 1 test from test_async (1005 ms total)

Error log

• Investigated issue
• Fixed test
• Followup issues created if necessary