fix(ci): fix flaky barrier read e2e transaction test (#18346)

e2e_test/batch/transaction/now.slt

@@ -7,26 +7,36 @@ create view v as select * from t where ts at time zone 'utc' >= now();
 statement ok
 create materialized view mv as select * from v;
 
+connection txn
+statement ok
+SET VISIBILITY_MODE TO checkpoint;
+
+connection txn
 statement ok
 insert into t select * from generate_series(
     now() at time zone 'utc' - interval '10' second,
     now() at time zone 'utc' + interval '20' second,
     interval '1' second / 20
 );
 
+connection txn
 statement ok
 flush;
 
+connection txn
 statement ok
 start transaction read only;
 
 # the view should not be empty, so that the following check is meaningful
+connection txn
 query T
 select count(*) > 0 from mv;
 ----
 t
 
 # the result from batch query and materialized view should be the same
+skipif in-memory
+connection txn
 query T
 select * from v
 except
@@ -40,6 +50,7 @@ select * from mv;
 ## select * from v;
 ## ----
 
+connection txn
 statement ok
 commit;
 

e2e_test/batch/transaction/read_only_multi_conn.slt

@@ -1,9 +1,11 @@
 statement ok
 create table t (v int);
 
+connection txn
 statement ok
 insert into t values (1), (2);
 
+connection txn
 statement ok
 flush;
 
@@ -15,6 +17,7 @@ connection txn
 statement ok
 start transaction read only;
 
+skipif in-memory
 connection txn
 query I
 select count(*) from t;
@@ -26,6 +29,7 @@ connection other
 statement ok
 flush;
 
+skipif in-memory
 connection other
 query I
 select count(*) from t;
@@ -41,13 +45,15 @@ statement ok
 flush;
 
 # inserts are visible in the `other` connection,
+skipif in-memory
 connection other
 query I
 select count(*) from t;
 ----
 3
 
 # ...but not in the read-only transaction
+skipif in-memory
 connection txn
 query I
 select count(*) from t;
@@ -59,6 +65,7 @@ statement ok
 flush;
 
 # still invisible even after flush
+skipif in-memory
 connection txn
 query I
 select count(*) from t;
@@ -70,6 +77,7 @@ statement ok
 commit;
 
 # now visible outside the transaction
+skipif in-memory
 connection txn
 query I
 select count(*) from t;