rcc

feat: Use string as default for unknown column type #1490

Job	Run time
Smoke test: stock R	4m 8s
pkgdown	2m 43s
windows-latest (release)	6m 23s
macos-latest (release)	6m 18s
windows-latest (4.1)	6m 23s
ubuntu-20.04 (release)	5m 56s
windows-latest (4.2)	6m 22s
ubuntu-22.04 (devel)	4m 35s
ubuntu-22.04 (release) with covr	6m 5s
ubuntu-22.04 (oldrel-1)	3m 35s
ubuntu-22.04 (oldrel-2)	3m 46s
ubuntu-22.04 (oldrel-3)	3m 46s
ubuntu-22.04 (oldrel-4)	4m 18s
macOS-latest (release) mariadb_config	6m 17s
macOS-latest (release) mysql_config	6m 17s
ubuntu-22.04 (release) MySQL server + client	3m 16s
ubuntu-22.04 (release) MariaDB server, MySQL client	3m 19s
ubuntu-22.04 (release) MySQL server, MariaDB client	4m 3s
ubuntu-22.04 (release) MariaDB server + client	3m 48s
	1h 31m 18s

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