patch 8.2.2780: Vim9: for loop over blob doesn't work

Problem:    Vim9: for loop over blob doesn't work.
Solution:   Make it work.
diff --git a/src/testdir/test_blob.vim b/src/testdir/test_blob.vim
index 21f90ef..fa482b4 100644
--- a/src/testdir/test_blob.vim
+++ b/src/testdir/test_blob.vim
@@ -283,33 +283,36 @@
 endfunc
 
 func Test_blob_for_loop()
-  let blob = 0z00010203
-  let i = 0
-  for byte in blob
-    call assert_equal(i, byte)
-    let i += 1
-  endfor
-    call assert_equal(4, i)
+  let lines =<< trim END
+      VAR blob = 0z00010203
+      VAR i = 0
+      for byte in blob
+        call assert_equal(i, byte)
+        LET i += 1
+      endfor
+      call assert_equal(4, i)
 
-  let blob = 0z00
-  call remove(blob, 0)
-  call assert_equal(0, len(blob))
-  for byte in blob
-    call assert_error('loop over empty blob')
-  endfor
-
-  let blob = 0z0001020304
-  let i = 0
-  for byte in blob
-    call assert_equal(i, byte)
-    if i == 1
+      LET blob = 0z00
       call remove(blob, 0)
-    elseif i == 3
-      call remove(blob, 3)
-    endif
-    let i += 1
-  endfor
-  call assert_equal(5, i)
+      call assert_equal(0, len(blob))
+      for byte in blob
+        call assert_report('loop over empty blob')
+      endfor
+
+      LET blob = 0z0001020304
+      LET i = 0
+      for byte in blob
+        call assert_equal(i, byte)
+        if i == 1
+          call remove(blob, 0)
+        elseif i == 3
+          call remove(blob, 3)
+        endif
+        LET i += 1
+      endfor
+      call assert_equal(5, i)
+  END
+  call CheckLegacyAndVim9Success(lines)
 endfunc
 
 func Test_blob_concatenate()