* bump nimbus-build-system to use Nim v2.0.6
* fix: update name and hash for csources of Nim v2
Otherwise we get errors like:
```
Building: Nim compiler
/build/source/vendor/nimbus-build-system/vendor/Nim /build/source
cmd: git clone -q --depth 1 -b master https://github.com/nim-lang/csources_v2.git csources_v2
24.6.0-dirty
cmd: cd csources_v2
ci/funs.sh: line 10: cd: csources_v2: No such file or directory
make[1]: *** [vendor/nimbus-build-system/makefiles/targets.mk:81: build-nim] Error 1
```
Also need to add source for `checksums` repository.
Signed-off-by: Jakub Sokołowski <jakub@status.im>
---------
Signed-off-by: Jakub Sokołowski <jakub@status.im>
Co-authored-by: Jakub Sokołowski <jakub@status.im>
tersec