patch 8.2.0672: heredoc in scripts does not accept lower case marker

Problem:    Heredoc in scripts does not accept lower case marker.
Solution:   Allow lower case only in non-Vim scripts. (Ken Takata,
            closes #6019)
diff --git a/src/evalvars.c b/src/evalvars.c
index 7c8b9f7..f6f0779 100644
--- a/src/evalvars.c
+++ b/src/evalvars.c
@@ -595,7 +595,7 @@
 	    return NULL;
 	}
 	*p = NUL;
-	if (vim_islower(*marker))
+	if (!script_get && vim_islower(*marker))
 	{
 	    emsg(_("E221: Marker cannot start with lower case letter"));
 	    return NULL;