Allow running nimble test in dependencies in the vendor forlder

config.nims

@@ -1,8 +1,13 @@
 import strutils
 
-when getEnv("NIMBUS_BUILD_SYSTEM") == "yes" and
+const currentDir = currentSourcePath()[0 .. ^(len("config.nims") + 1)]
-     system.fileExists("nimbus-build-system.paths"):
+
-  --noNimblePath
+if getEnv("NIMBUS_BUILD_SYSTEM") == "yes" and
+   # BEWARE
+   # In Nim 1.6, config files are evaluated with a working directory
+   # matching where the Nim command was invocated. This means that we
+   # must do all file existance checks with full absolute paths:
+   system.fileExists(currentDir & "nimbus-build-system.paths"):
   include "nimbus-build-system.paths"
 
 if defined(release):