patch 8.2.4087: cannot test items from an autoload script easily

Problem:    Cannot test items from an autoload script easily.
Solution:   Add the "autoload" value for test_override().
diff --git a/runtime/doc/testing.txt b/runtime/doc/testing.txt
index 44296f0..3ff1450 100644
--- a/runtime/doc/testing.txt
+++ b/runtime/doc/testing.txt
@@ -188,23 +188,25 @@
 		to run tests. Only to be used for testing Vim!
 		The override is enabled when {val} is non-zero and removed
 		when {val} is zero.
-		Current supported values for name are:
+		Current supported values for {name} are:
 
-		name	     effect when {val} is non-zero ~
-		redraw       disable the redrawing() function
-		redraw_flag  ignore the RedrawingDisabled flag
+		{name}	     effect when {val} is non-zero ~
+		autoload     `import autoload` will load the script right
+			     away, not postponed until an item is used
 		char_avail   disable the char_avail() function
-		starting     reset the "starting" variable, see below
 		nfa_fail     makes the NFA regexp engine fail to force a
 			     fallback to the old engine
 		no_query_mouse  do not query the mouse position for "dec"
 				terminals
 		no_wait_return	set the "no_wait_return" flag.  Not restored
 				with "ALL".
-		ui_delay     time in msec to use in ui_delay(); overrules a
-			     wait time of up to 3 seconds for messages
+		redraw       disable the redrawing() function
+		redraw_flag  ignore the RedrawingDisabled flag
+		starting     reset the "starting" variable, see below
 		term_props   reset all terminal properties when the version
 			     string is detected
+		ui_delay     time in msec to use in ui_delay(); overrules a
+			     wait time of up to 3 seconds for messages
 		uptime 	     overrules sysinfo.uptime
 		ALL	     clear all overrides ({val} is not used)