patch 8.2.1867: Vim9: argument to add() not checked for blob

Problem:    Vim9: argument to add() not checked for blob.
Solution:   Add the BLOBAPPEND instruction.
diff --git a/src/testdir/test_vim9_disassemble.vim b/src/testdir/test_vim9_disassemble.vim
index fe1ce66..97797bc 100644
--- a/src/testdir/test_vim9_disassemble.vim
+++ b/src/testdir/test_vim9_disassemble.vim
@@ -301,6 +301,34 @@
         res)
 enddef
 
+def s:BlobAdd()
+  var b: blob = 0z
+  add(b, 123)
+  add(b, g:aNumber)
+enddef
+
+def Test_disassemble_blob_add()
+  var res = execute('disass s:BlobAdd')
+  assert_match('<SNR>\d*_BlobAdd\_s*' ..
+        'var b: blob = 0z\_s*' ..
+        '\d PUSHBLOB 0z\_s*' ..
+        '\d STORE $0\_s*' ..
+        'add(b, 123)\_s*' ..
+        '\d LOAD $0\_s*' ..
+        '\d PUSHNR 123\_s*' ..
+        '\d BLOBAPPEND\_s*' ..
+        '\d DROP\_s*' ..
+        'add(b, g:aNumber)\_s*' ..
+        '\d LOAD $0\_s*' ..
+        '\d\+ LOADG g:aNumber\_s*' ..
+        '\d\+ CHECKTYPE number stack\[-1\]\_s*' ..
+        '\d\+ BLOBAPPEND\_s*' ..
+        '\d\+ DROP\_s*' ..
+        '\d\+ PUSHNR 0\_s*' ..
+        '\d\+ RETURN',
+        res)
+enddef
+
 def s:ScriptFuncUnlet()
   g:somevar = "value"
   unlet g:somevar