Enable push diagnostic nofications by default.

It looks like that a lot of editors don't actually pull request
diagnostics, so let push diagnostics on by default.

Fixes: #2434

verible/verilog/tools/ls/verible-verilog-ls.cc

diff --git a/verible/verilog/tools/ls/verible-verilog-ls.cc b/verible/verilog/tools/ls/verible-verilog-ls.cc
index d3099f3..cd10f90 100644
--- a/verible/verilog/tools/ls/verible-verilog-ls.cc
+++ b/verible/verilog/tools/ls/verible-verilog-ls.cc
@@ -31,9 +31,9 @@
 #define read(fd, buf, size) _read(fd, buf, size)
 #endif
 
-// These days, editors mostly request the diagnostic and don't want them
-// as notification (in fact, they might show it multiple times)
-ABSL_FLAG(bool, push_diagnostic_notifications, false,
+// If an editor shows the diagnostics multiple times, then this might be
+// because it merges the push notifications with the pull requests it does.
+ABSL_FLAG(bool, push_diagnostic_notifications, true,
           "Send diagnostic as notifications.");
 
 // Since it is hard to see what exactly the editor passes to the language