editable: exit script with callable return

This change ensures that generated scripts for editable package 
installs exit using return value from callable used.

poetry/masonry/builders/editable.py

@@ -27,10 +27,11 @@ if TYPE_CHECKING:
 
 SCRIPT_TEMPLATE = """\
 #!{python}
+import sys
 from {module} import {callable_holder}
 
 if __name__ == '__main__':
-    {callable_}()
+    sys.exit({callable_}())
 """
 
 WINDOWS_CMD_TEMPLATE = """\

tests/masonry/builders/test_editable_builder.py

@@ -148,10 +148,11 @@ My Package
 
     baz_script = """\
 #!{python}
+import sys
 from bar import baz
 
 if __name__ == '__main__':
-    baz.boom.bim()
+    sys.exit(baz.boom.bim())
 """.format(
         python=tmp_venv.python
     )
@@ -160,10 +161,11 @@ if __name__ == '__main__':
 
     foo_script = """\
 #!{python}
+import sys
 from foo import bar
 
 if __name__ == '__main__':
-    bar()
+    sys.exit(bar())
 """.format(
         python=tmp_venv.python
     )
@@ -172,10 +174,11 @@ if __name__ == '__main__':
 
     fox_script = """\
 #!{python}
+import sys
 from fuz.foo import bar
 
 if __name__ == '__main__':
-    bar.baz()
+    sys.exit(bar.baz())
 """.format(
         python=tmp_venv.python
     )