[ci] Made the CI pipeline more legible by adding a separate nix build target.

3 jobs for downstream-refactor in 12 seconds (queued for 2 seconds)
Status Job ID Name Coverage
  Build
failed #16429
integration
libnrm.build

00:00:12

 
  Test
skipped #16430
integration
helloworld.integration.test
skipped #16431
integration
perfwrapper.integration.test
 
Name Stage Failure
failed
libnrm.build Build
                             ^~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
make[2]: *** [Makefile:468: downstream_api.lo] Error 1
make[2]: Leaving directory '/build/libnrm/src'
make[1]: *** [Makefile:344: all] Error 2
make[1]: Leaving directory '/build/libnrm/src'
make: *** [Makefile:443: all-recursive] Error 1
builder for '/nix/store/66cx9w74srjfnhrk42gd2gm232rgdwc5-libnrm.drv' failed with exit code 2
error: build of '/nix/store/66cx9w74srjfnhrk42gd2gm232rgdwc5-libnrm.drv' failed
ERROR: Job failed: exit status 1