Fix testcase for invalid value at node initialization

[christophfroehlich]

Since PickNikRobotics/generate_parameter_library#339 the behavior of generate_parameter_library changed.
The parameter in the testcase can't even be declared as zero now (earlier it was declared with 0 but the validator failed later).

2026-05-18T07:35:36.9553861Z     [ RUN      ] FilterTest.TestLowPassWrenchFilterInvalidThenFixedParameter
2026-05-18T07:35:36.9555026Z     [ERROR] [1779089735.022610158] [TestLowPassWrenchFilterInvalidThenFixedParameter.TestLowPassFilter]: LowPass filter cannot be configured: parameter 'sampling_frequency' could not be set: Parameter {sampling_frequency} doesn't comply with floating point range. (type : N6rclcpp10exceptions30InvalidParameterValueExceptionE)
2026-05-18T07:35:36.9556068Z     unknown file: Failure
2026-05-18T07:35:36.9556522Z     C++ exception with description "parameter 'sampling_frequency' cannot be set because it was not declared" thrown in the test body.
2026-05-18T07:35:36.9556934Z     
2026-05-18T07:35:36.9557232Z     [  FAILED  ] FilterTest.TestLowPassWrenchFilterInvalidThenFixedParameter (7 ms)

Is this user-facing behavior change?

no

Did you use Generative AI?

no