patch 8.2.3284: no error for insert() or remove() changing a locked blob

Problem:    No error for insert() or remove() changing a locked blob.
Solution:   Check a blob is not locked before changing it. (Sean Dewar,
            closes #8696)

src/testdir/test_blob.vim

@@ -428,6 +428,23 @@ func Test_blob_func_remove()
       call remove(test_null_blob(), 1, 2)
   END
   call CheckLegacyAndVim9Failure(lines, 'E979:')
+
+  let lines =<< trim END
+      let b = 0zDEADBEEF
+      lockvar b
+      call remove(b, 0)
+      unlockvar b
+  END
+  call CheckScriptFailure(lines, 'E741:')
+
+  " can only check at script level, not in a :def function
+  let lines =<< trim END
+      vim9script
+      var b = 0zDEADBEEF
+      lockvar b
+      remove(b, 0)
+  END
+  call CheckScriptFailure(lines, 'E741:')
 endfunc
 
 func Test_blob_read_write()
@@ -543,6 +560,22 @@ func Test_blob_insert()
       insert(test_null_blob(), 0x33)
   END
   call CheckDefExecAndScriptFailure(lines, 'E1131:')
+
+  let lines =<< trim END
+      let b = 0zDEADBEEF
+      lockvar b
+      call insert(b, 3)
+      unlockvar b
+  END
+  call CheckScriptFailure(lines, 'E741:')
+
+  let lines =<< trim END
+      vim9script
+      var b = 0zDEADBEEF
+      lockvar b
+      insert(b, 3)
+  END
+  call CheckScriptFailure(lines, 'E741:')
 endfunc
 
 func Test_blob_reverse()