crdb_interal: always report non-null fraction fraction_completed

We have code that assumes it can always scan this into a float, which
isn't the case when it is NULL.

Epic: none
Release note: None

Author: stevendanna

pkg/sql/crdb_internal.go

@@ -1035,7 +1035,7 @@ var crdbInternalJobsView = virtualSchemaView{
 		j.created::timestamptz,
 		j.finished,
 		greatest(j.created, j.finished, p.written, s.written)::timestamptz AS modified,
-		p.fraction as fraction_completed,
+		coalesce(p.fraction, 0)::FLOAT as fraction_completed,
 		p.resolved as high_water_timestamp,
 		coalesce(j.error_msg, '') as error,
 		j.claim_instance_id as coordinator_id

pkg/sql/opt/exec/execbuilder/testdata/explain

@@ -121,7 +121,7 @@ distribution: local
 vectorized: true
 ·
 • sort
-│ order: -column70,-created
+│ order: -column71,-created
 │
 └── • render
     │