patch 8.2.2925: Vim9: line continuation comment uses legacy syntax

Problem:    Vim9: line continuation comment uses legacy syntax.
Solution:   Check for #\ instead of "\. (closes #8295)

src/scriptfile.c

@@ -1842,7 +1842,8 @@ getsourceline(
 			ga_concat(&ga, p);
 		    }
 		}
-		else if (!(p[0] == '"' && p[1] == '\\' && p[2] == ' ')
+		else if (!(p[0] == (in_vim9script() ? '#' : '"')
+						&& p[1] == '\\' && p[2] == ' ')
 		     && !(do_vim9_all && (*p == NUL || vim9_comment_start(p))))
 		    break;
 		/* drop a # comment or "\ comment line */

src/testdir/test_vim9_script.vim

@@ -3074,6 +3074,24 @@ def Test_vim9_comment()
       'func Test() # comment',
       'endfunc',
       ], 'E488:')
+
+  var lines =<< trim END
+      vim9script
+      syn region Text
+      \ start='foo'
+      #\ comment
+      \ end='bar'
+  END
+  CheckScriptSuccess(lines)
+
+  lines =<< trim END
+      vim9script
+      syn region Text
+      \ start='foo'
+      "\ comment
+      \ end='bar'
+  END
+  CheckScriptFailure(lines, 'E399:')
 enddef
 
 def Test_vim9_comment_gui()

src/version.c

@@ -750,6 +750,8 @@ static char *(features[]) =
 
 static int included_patches[] =
 {   /* Add new patch number below this line */
+/**/
+    2925,
 /**/
     2924,
 /**/