VariantQueue does not implement setCapacity for FiFo_SingleProducerSingleConsumer

## Required information

**Operating system:**
all

**Compiler version:**
all

**cmake flags:**
-DONE_TO_MANY_ONLY=ON

**Observed result or behaviour:**

running `./posh_moduletests --gtest_filter=PoshRuntime_test.GetMiddlewareSubscriberWithQueueFullPolicySetToBlockPublisherLeadsToBlockPublisher` results in a `SIGABRT`

**Expected result or behaviour:**
Test should pass

**Conditions where it occurred / Performed steps:**

From `variant_queu.inl`
```cpp
case VariantQueueTypes::FiFo_SingleProducerSingleConsumer:
{
/// @todo must be implemented for FiFo
assert(false);
return false;
}
```

Start in variant_queu.inl at the FiFo_SingleProducerSingleConsumer branch of setCapacity, then run posh_moduletests with the PoshRuntime_test.GetMiddlewareSubscriberWithQueueFullPolicySetToBlockPublisherLeadsToBlockPublisher filter. The work is done when this queue type no longer aborts and the test passes with -DONE_TO_MANY_ONLY=ON.

Written by the indexing model from the issue text.