CI/OpenBSD: run functional tests

Adapt some tests for OpenBSD:

- scrollback_spec:
  - seq(1) is not available on OpenBSD: we'd use jot(1).
  - Instead use a (hopefully) portable awk(1) snippet.
- channels_spec
- job_spec
- tui_spec

test/functional/terminal/scrollback_spec.lua

@@ -406,7 +406,7 @@ describe("'scrollback' option", function()
     if iswin() then
       feed_data('for /L %I in (1,1,30) do @(echo line%I)\r')
     else
-      feed_data('for i in $(seq 1 30); do echo "line$i"; done\n')
+      feed_data('awk "BEGIN{for(n=1;n<=30;n++) print \\\"line\\\" n}"\n')
     end
     screen:expect{any='line30                        '}
     retry(nil, nil, function() expect_lines(7) end)
@@ -431,7 +431,7 @@ describe("'scrollback' option", function()
     if iswin() then
       feed_data('for /L %I in (1,1,30) do @(echo line%I)\r')
     else
-      feed_data('for i in $(seq 1 30); do echo "line$i"; done\n')
+      feed_data('awk "BEGIN{for(n=1;n<=30;n++) print \\\"line\\\" n}"\n')
     end
 
     screen:expect{any='line30                        '}
@@ -448,7 +448,7 @@ describe("'scrollback' option", function()
     if iswin() then
       feed_data('for /L %I in (1,1,40) do @(echo line%I)\r')
     else
-      feed_data('for i in $(seq 1 40); do echo "line$i"; done\n')
+      feed_data('awk "BEGIN{for(n=1;n<=40;n++) print \\\"line\\\" n}"\n')
     end
 
     screen:expect{any='line40                        '}

test/functional/terminal/tui_spec.lua

@@ -1203,7 +1203,9 @@ describe("TUI 'term' option", function()
   end)
 
   it('gets system-provided term if $TERM is valid', function()
-    if is_bsd then  -- BSD lacks terminfo, builtin is always used.
+    if string.lower(uname()) == "openbsd" then
+      assert_term("xterm", "xterm")
+    elseif is_bsd then  -- BSD lacks terminfo, builtin is always used.
       assert_term("xterm", "builtin_xterm")
     elseif is_macos then
       local status, _ = pcall(assert_term, "xterm", "xterm")