Enable random bitmaps to work with serialisation checks

#### Description:

https://github.com/BHoM/Test_Toolkit/pull/521/files#diff-03be553eb97d204baf9c5bc320e7bf76ca3c636ed893555a5e49da2fe522a390 introduced random bitmaps. This is at arbitrary times causing issues with the serialisation check.

See:
https://github.com/BuroHappoldEngineering/Forms_Toolkit/pull/231/checks?check_run_id=50458125010

And is therefore being turned off
#525

Should investigate this better to enable it to function rather than turning off.

When enabled, should also make sure to check the properties of bitmap type in the dummy object test.

See https://github.com/BHoM/Test_Toolkit/pull/527/files for how test was changed, and is to be reverted.

Start with the random bitmap change in Test_Toolkit PR #521 and reproduce the serialization failure shown in Forms_Toolkit PR #231. Compare the dummy object test changes in Test_Toolkit PR #527, then determine why bitmap properties fail intermittently and restore their property checks when serialization succeeds.

Written by the indexing model from the issue text.