[C] Fix typo in gbode (#11283) (#11297)

The single rate solver could not get out of the loop because `err`
was not set correctly.

Fixes #11280

Co-authored-by: bernhardbachmann <bernhardbachmann@users.noreply.github.com>
(cherry picked from commit 9613f29)

OMCompiler/SimulationRuntime/c/simulation/solver/gbode_main.c

@@ -1776,7 +1776,7 @@ int gbode_singlerate(DATA *data, threadData_t *threadData, SOLVER_INFO *solverIn
         gbData->stepSizeValues[i] = gbData->stepSizeValues[i - 1];
       }
       // update new values
-      gbData->errValues[0] = _omc_gen_maximumVectorNorm(gbData->err, nStates);
+      gbData->errValues[0] = err = _omc_gen_maximumVectorNorm(gbData->err, nStates);
       gbData->stepSizeValues[0] = gbData->stepSize;
 
       // Store performed step size for latter interpolation