Force track_io_timing off in explain.sql to avoid failures when enabled.

Discussion: https://postgr.es/m/20201029231037.rkxo57ugnuchykpu@alap3.anarazel.de

src/test/regress/expected/explain.out

@@ -47,9 +47,12 @@ begin
     return data::jsonb;
 end;
 $$;
--- Also, disable JIT, or we'll get different output on machines
--- where that's been forced on
+-- Disable JIT, or we'll get different output on machines where that's been
+-- forced on
 set jit = off;
+-- Similarly, disable track_io_timing, to avoid output differences when
+-- enabled.
+set track_io_timing = off;
 -- Simple cases
 select explain_filter('explain select * from int8_tbl i8');
                      explain_filter                      

src/test/regress/sql/explain.sql

@@ -51,10 +51,13 @@ begin
 end;
 $$;
 
--- Also, disable JIT, or we'll get different output on machines
--- where that's been forced on
+-- Disable JIT, or we'll get different output on machines where that's been
+-- forced on
 set jit = off;
 
+-- Similarly, disable track_io_timing, to avoid output differences when
+-- enabled.
+set track_io_timing = off;
 
 -- Simple cases