patch 8.2.0754: Vim9: No test for forward declaration

Problem:    Vim9: No test for forward declaration.
Solution:   Add a test.
diff --git a/src/testdir/test_vim9_script.vim b/src/testdir/test_vim9_script.vim
index c528b80..6b6228e 100644
--- a/src/testdir/test_vim9_script.vim
+++ b/src/testdir/test_vim9_script.vim
@@ -1732,6 +1732,7 @@
   END
   writefile(lines, 'Xfinished')
   source Xfinished
+  " GetValue() is not called during discovery phase
   assert_equal(1, g:count)
 
   unlet g:count
@@ -1752,6 +1753,28 @@
   delete('Xfinished')
 enddef
 
+def Test_forward_declaration()
+  let lines =<< trim END
+    vim9script
+    g:initVal = GetValue()
+    def GetValue(): string
+      return theVal
+    enddef
+    let theVal = 'something'
+    theVal = 'else'
+    g:laterVal = GetValue()
+  END
+  writefile(lines, 'Xforward')
+  source Xforward
+  assert_equal('something', g:initVal)
+  assert_equal('else', g:laterVal)
+
+  unlet g:initVal
+  unlet g:laterVal
+  delete('Xforward')
+enddef
+
+
 " Keep this last, it messes up highlighting.
 def Test_substitute_cmd()
   new
diff --git a/src/version.c b/src/version.c
index ad56b7a..8ff5161 100644
--- a/src/version.c
+++ b/src/version.c
@@ -747,6 +747,8 @@
 static int included_patches[] =
 {   /* Add new patch number below this line */
 /**/
+    754,
+/**/
     753,
 /**/
     752,