If upgrade from read to write transaction fails, don't roll back the
transaction. Instead restore the transaction into its original state,
which allows deferred transactions that have not read anything to
restart automatically.
Fixes#2984
`BTreeTable::to_sql` makes us incompatible with SQLite by losing e.g. the original whitespace provided during the CREATE TABLE command.
For now let's fix our tests by regex-replacing every CREATE TABLE in
the entire repo to have exactly 1 space after the table name in the
CREATE TABLE statement.
