CI: Update FreeBSD image version for Cirrus runner. #3314

Job	Run time
cmake-offline-googletest	4m 1s
cmake-offline-googletest-src	3m 57s
system-sexpp, sexpp shared libs on, rnp shared libs on	2m 53s
package-source	26s
system-sexpp, sexpp shared libs on, rnp shared libs off	2m 48s
system-sexpp, sexpp shared libs off, rnp shared libs on	2m 55s
ubuntu-latest [CC gcc; botan; shared libs on; GnuPG stable]	3m 59s
system-sexpp, sexpp shared libs off, rnp shared libs off	2m 53s
ubuntu-latest [CC clang; botan; shared libs on; GnuPG stable]	4m 6s
ubuntu-latest [CC gcc; openssl; shared libs on; GnuPG stable]	4m 17s
ubuntu-latest [CC clang; openssl; shared libs on; GnuPG stable]	4m 17s
ubuntu-20.04 [CC gcc; openssl; shared libs on; GnuPG stable]	3m 39s
ubuntu-latest [CC gcc; botan; shared libs off; GnuPG stable]	4m 17s
package	1m 14s
debian-tests	8s
	45m 50s

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