[BUG]: vsomeip/tests cannot build when ENABLE_MULTIPLE_ROUTING_MANAGERS is enabled

### vSomeip Version

c70ced40c75a9

### Boost Version

1.82

### Environment

gcc

### Describe the bug

If `ENABLE_MULTIPLE_ROUTING_MANAGERS` is enabled, vsomeip won't configure due to the following.

```
CMake Error at test/CMakeLists.txt:64 (add_library):
Error evaluating generator expression:

$

Objects of target "vsomeip3-cfg-internal" referenced but no such target
exists.

CMake Error at test/CMakeLists.txt:64 (add_library):
Error evaluating generator expression:

$

Objects of target "vsomeip3-cfg-internal" referenced but no such target
exists.

CMake Error at test/CMakeLists.txt:64 (add_library):
Error evaluating generator expression:

$

Objects of target "vsomeip3-cfg-internal" referenced but no such target
exists.

CMake Error at test/CMakeLists.txt:64 (add_library):
No SOURCES given to target: vsomeip3-cfg-test
```

I understand that no one else seems to use `ENABLE_MULTIPLE_ROUTING_MANAGERS` and it must be disabled to build the tests, but this happens right out of the box.

### Reproduction Steps

Configure with:
```
cmake -DENABLE_MULTIPLE_ROUTING_MANAGERS="ON" -DGTEST_ROOT="${HOME}.conan2/p/gtestd6582aeef6243/p" -DCMAKE_POLICY_DEFAULT_CMP0091="NEW" -DCMAKE_BUILD_TYPE="RelWithDebInfo" vsomeip-source
```
(with your own gtest directory of course)

### Expected behaviour

Successful configuration

### Logs and Screenshots

_No response_

Inspect test/CMakeLists.txt around line 64 and the conditional definition of vsomeip3-cfg-internal when ENABLE_MULTIPLE_ROUTING_MANAGERS is enabled. Reproduce the issue with the provided CMake configuration, then verify configuration succeeds and vsomeip3-cfg-test receives its sources.

Written by the indexing model from the issue text.