rcc

feat: Use string as default for unknown column type #1493

Job	Run time
Smoke test: stock R	3m 8s
windows-latest (release)	9m 9s
windows-latest (4.1)	11m 51s
macos-latest (release)	6m 37s
pkgdown	3m 6s
windows-latest (4.2)	12m 10s
ubuntu-20.04 (release)	5m 51s
ubuntu-22.04 (devel)	4m 43s
ubuntu-22.04 (release) with covr	6m 21s
ubuntu-22.04 (oldrel-1)	3m 21s
ubuntu-22.04 (oldrel-2)	4m 4s
ubuntu-22.04 (oldrel-3)	3m 52s
ubuntu-22.04 (oldrel-4)	3m 59s
macOS-latest (release) mariadb_config	6m 13s
macOS-latest (release) mysql_config	8m 35s
ubuntu-22.04 (release) MySQL server + client	3m 22s
ubuntu-22.04 (release) MariaDB server, MySQL client	4m 7s
ubuntu-22.04 (release) MySQL server, MariaDB client	3m 19s
ubuntu-22.04 (release) MariaDB server + client	3m 26s
	1h 47m 14s

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