patch 8.0.1780: test fails because Vim in a terminal uses wrong 'encoding'

Problem:    Test fails because Vim in a terminal uses wrong 'encoding'.
Solution:   Set encoding in the test where it matters. (James McCoy,
            closes #2847)

Author: brammool

src/testdir/test_terminal.vim

@@ -1011,7 +1011,7 @@ func Test_terminal_dumpwrite_composing()
 
   let text = " a\u0300 e\u0302 o\u0308"
   call writefile([text], 'Xcomposing')
-  let buf = RunVimInTerminal('Xcomposing', {})
+  let buf = RunVimInTerminal('--cmd "set encoding=utf-8" Xcomposing', {})
   call WaitForAssert({-> assert_match(text, term_getline(buf, 1))})
   call term_dumpwrite(buf, 'Xdump')
   let dumpline = readfile('Xdump')[0]

src/version.c

@@ -761,6 +761,8 @@ static char *(features[]) =
 
 static int included_patches[] =
 {   /* Add new patch number below this line */
+/**/
+    1780,
 /**/
     1779,
 /**/