fix(test): close tester in avm_check_circuit_custom_bc truncation afterEach

Same teardown leak as in simulator/.../apps_tests/custom_bc.test.ts:
the third describe block's afterEach was missing await tester.close(),
leaving the AvmProvingTester (which spawns an AvmSimulatorPool + CdbIpcServer)
alive. Jest could not exit after the suite completed and was killed at the
600s CI timeout.

Author: charlielye

yarn-project/bb-prover/src/avm_proving_tests/avm_check_circuit_custom_bc.test.ts

@@ -112,6 +112,7 @@ describe('AVM custom bytecodes truncation', () => {
   });
 
   afterEach(async () => {
+    await tester.close();
     await worldStateService.close();
   });