src/sage/tests/startup.py: Hide a legitimate .all import from relint

Author: Matthias Koeppe

src/sage/tests/startup.py

@@ -6,7 +6,8 @@
 not work. Instead, we test this by starting a new Python process::
 
     sage: from sage.tests.cmdline import test_executable
-    sage: cmd = "from sage.all import *\nprint('IPython' in sys.modules)\n"
+    sage: environment = "sage.all"
+    sage: cmd = f"from {environment} import *\nprint('IPython' in sys.modules)\n"
     sage: print(test_executable(["sage", "--python"], cmd)[0])  # long time
     False