patch 8.2.0658: HP-UX build fails when setenv() is not defined

Problem:    HP-UX build fails when setenv() is not defined.
Solution:   Change "colors" to "t_colors". (John Marriott)
diff --git a/src/os_unix.c b/src/os_unix.c
index 66903e0..f8fe2cb 100644
--- a/src/os_unix.c
+++ b/src/os_unix.c
@@ -4196,7 +4196,7 @@
     vim_snprintf(envbuf_Columns, sizeof(envbuf_Columns),
 						       "COLUMNS=%ld", columns);
     putenv(envbuf_Columns);
-    vim_snprintf(envbuf_Colors, sizeof(envbuf_Colors), "COLORS=%ld", colors);
+    vim_snprintf(envbuf_Colors, sizeof(envbuf_Colors), "COLORS=%ld", t_colors);
     putenv(envbuf_Colors);
 #  ifdef FEAT_TERMINAL
     if (is_terminal)