Alonzo test failure: Missing script witnesses

On commit dd13fada:
```
Build profile: -w ghc-8.10.7 -O1
In order, the following will be built (use -v for more details):
- cardano-ledger-alonzo-test-0.1.0.0 (test:cardano-ledger-alonzo-test) (first run)
Preprocessing test suite 'cardano-ledger-alonzo-test' for cardano-ledger-alonzo-test-0.1.0.0..
Building test suite 'cardano-ledger-alonzo-test' for cardano-ledger-alonzo-test-0.1.0.0..
Running 1 test suites...
Test suite cardano-ledger-alonzo-test: RUNNING...

Running in scenario: Development
Alonzo tests
Fast Alonzo Property Tests
total amount of Ada is preserved (Chain):
Discarded trace: TotExUnits violation: genEraTweakBlock: AlonzoEraGen.hs

Discarded trace: MinFeee violation: genEraDne: AlonzoEraGen.hs

Discarded trace: No inputs left. Utxo.hs

Discarded trace: NoMoneyleft Utxo.hs
FAIL (74.43s)
*** Failed! (after 36 tests):
Exception while generating shrink-list:
LEDGER sigGen: [UtxowFailure (WrappedShelleyEraFailure (MissingScriptWitnessesUTXOW (fromList [])))]
CallStack (from HasCallStack):
error, called at src/Test/Cardano/Ledger/Shelley/Generator/Trace/Ledger.hs:179:24 in cardano-ledger-shelley-test-0.1.0.0-inplace:Test.Cardano.Ledger.Shelley.Generator.Trace.Ledger
genAndApplyTx, called at src/Test/Cardano/Ledger/Shelley/Generator/Trace/Ledger.hs:159:11 in cardano-ledger-shelley-test-0.1.0.0-inplace:Test.Cardano.Ledger.Shelley.Generator.Trace.Ledger
sigGen, called at src/Test/Cardano/Ledger/Shelley/Generator/Block.hs:101:16 in cardano-ledger-shelley-test-0.1.0.0-inplace:Test.Cardano.Ledger.Shelley.Generator.Block
Use --quickcheck-replay=970901 to reproduce.

1 out of 1 tests failed (74.46s)
Test suite cardano-ledger-alonzo-test: FAIL
Test suite logged to:
/home/work/Projects/cardano-ledger/dist-newstyle/build/x86_64-linux/ghc-8.10.7/cardano-ledger-alonzo-test-0.1.0.0/t/cardano-ledger-alonzo-test/test/cardano-ledger-alonzo-test-0.1.0.0-cardano-ledger-alonzo-test.log
0 of 1 test suites (0 of 1 test cases) passed.
```

Might be related to #2811