DynamicCapabilityClient: fix crash due to wrong types

[lewinb-corp]

In the last commit touching this line, a ')' was put in the wrong place, leading to errors like this one:

  File "capnp/lib/capnp.pyx", line 2172, in capnp.lib.capnp._DynamicCapabilityClient.__dir__
TypeError: unsupported operand type(s) for +: 'set' and 'tuple'

[haata]

@tobiasah Can you take a look at the Windows failure. I suspect something changed in the GitHub Actions windows-2019 os target and is either setting a variable or a dependency is missing.

The way it's supposed to work is cmake is supposed to auto-detect that it's a windows environment and use that build system. But for some reason ninja is being chosen (which probably isn't installed).