kicad-*: pin to protobuf_29

https://hydra.nixos.org/build/295636538/nixlog/8/tail
I tested that this fixes build of kicad-testing-small.
(some others were broken on nixpkgs master already)

Changed files
+2 -2
pkgs
applications
science
electronics
kicad
+2 -2
pkgs/applications/science/electronics/kicad/base.nix
···
opencascade-occt_7_6,
libngspice,
valgrind,
-
protobuf,
+
protobuf_29,
nng,
stable,
···
unixODBC
libdeflate
opencascade-occt
-
protobuf
+
protobuf_29
# This would otherwise cause a linking requirement for mbedtls.
(nng.override { mbedtlsSupport = false; })