Fix: cwd arg of fork_exec can be path-like

Author: fangerer

graalpython/com.oracle.graal.python/src/com/oracle/graal/python/builtins/modules/PosixSubprocessModuleBuiltins.java

@@ -344,6 +344,7 @@ int forkExecDefault(VirtualFrame frame, Object args, Object executable_list, Obj
                         @Cached CastToListNode castArgs,
                         @Cached CastToListNode castExecList,
                         @Cached CastToListNode castFdsToKeep,
+                        @CachedLibrary(limit = "1") PythonObjectLibrary cwdLib,
                         @Cached CastToJavaStringNode castCwd,
                         @Cached CastToListNode castEnv,
                         @CachedLibrary(limit = "3") PythonObjectLibrary lib) {
@@ -352,7 +353,7 @@ int forkExecDefault(VirtualFrame frame, Object args, Object executable_list, Obj
                 actualCwd = getContext().getEnv().getCurrentWorkingDirectory().getPath();
             } else {
                 try {
-                    actualCwd = castCwd.execute(cwd);
+                    actualCwd = castCwd.execute(cwdLib.asPathWithState(cwd, PArguments.getThreadState(frame)));
                 } catch (CannotCastException e) {
                     throw raise(PythonBuiltinClassType.TypeError, ErrorMessages.EXPECTED_S_P_FOUND, "bytes", cwd);
                 }