UI: rename "Toggle ..." back to "Show Markers"

Change made in recent show marker refactor dc87d09b8b

On writing docs the term "Show" makes more sense.

source/blender/makesrna/intern/rna_space.c

@@ -4821,7 +4821,7 @@ static void rna_def_space_dopesheet(BlenderRNA *brna)
   prop = RNA_def_property(srna, "show_pose_markers", PROP_BOOLEAN, PROP_NONE);
   RNA_def_property_boolean_sdna(prop, NULL, "flag", SACTION_POSEMARKERS_SHOW);
   RNA_def_property_ui_text(prop,
-                           "Toggle Pose Markers",
+                           "Show Pose Markers",
                            "Show markers belonging to the active action instead of Scene markers "
                            "(Action and Shape Key Editors only)");
   RNA_def_property_update(prop, NC_SPACE | ND_SPACE_DOPESHEET, NULL);