backupccl: possibly deflake TestBackupRestoreAppend

In CI we've seen this test fail with:

    backup_test.go:670: error scanning '&{<nil> 0xc019c5b580}': pq:
    restart transaction: TransactionRetryWithProtoRefreshError:
    TransactionRetryError: retry txn (RETRY_SERIALIZABLE - failed
    preemptive refresh): "sql txn" meta={id=77054b51 key=/Table/121/1
    pri=0.03587869 epo=0 ts=1689916873.568949604,1
    min=1689916873.436580640,0 seq=1000} lock=true stat=PENDING
    rts=1689916873.436580640,0 wto=false gul=1689916873.936580640,0

The `RETURNING` clauses on these two `UPDATE` statements prevent
automatic transaction retries.

Here we wrap the queries in an explicit transaction with a retry loop
which should prevent the test failure test, assuming that the update
isn't so contended it won't ever complete.

I am unable to stress this enough locally to reproduce this error.

Probably Fixes #107330

Epic: none

Release note: None

pkg/ccl/backupccl/backup_test.go

@@ -659,15 +659,18 @@ func TestBackupRestoreAppend(t *testing.T) {
 		sqlDB.ExpectErr(t, "A full backup cannot be written to \"/subdir\", a user defined subdirectory",
 			"BACKUP INTO $4 IN ($1, $2, $3) AS OF SYSTEM TIME "+tsBefore, append(test.collectionsWithSubdir, specifiedSubdir)...)
 
-		sqlDB.QueryRow(t, "UPDATE data.bank SET balance = 100 RETURNING cluster_logical_timestamp()").Scan(&ts1)
+		sqlDB.RunWithRetriableTxn(t, func(txn *gosql.Tx) error {
+			return txn.QueryRow("UPDATE data.bank SET balance = 100 RETURNING cluster_logical_timestamp()").Scan(&ts1)
+		})
 		sqlDB.Exec(t, "BACKUP INTO LATEST IN ($1, $2, $3) AS OF SYSTEM TIME "+ts1, test.collections...)
 
 		// Append to latest again, just to prove we can append to an appended one and
 		// that appended didn't e.g. mess up LATEST.
 		sqlDB.QueryRow(t, "SELECT cluster_logical_timestamp()").Scan(&ts1again)
 		sqlDB.Exec(t, "BACKUP INTO LATEST IN ($1, $2, $3) AS OF SYSTEM TIME "+ts1again, test.collections...)
-
-		sqlDB.QueryRow(t, "UPDATE data.bank SET balance = 200 RETURNING cluster_logical_timestamp()").Scan(&ts2)
+		sqlDB.RunWithRetriableTxn(t, func(txn *gosql.Tx) error {
+			return txn.QueryRow("UPDATE data.bank SET balance = 200 RETURNING cluster_logical_timestamp()").Scan(&ts2)
+		})
 		rowsTS2 := sqlDB.QueryStr(t, "SELECT * from data.bank ORDER BY id")
 
 		// Start a new full-backup in the collection version.