CI: Update FreeBSD image version for Cirrus runner. #3313

Job	Run time
cmake-offline-googletest	4m 6s
cmake-offline-googletest-src	4m 8s
system-sexpp, sexpp shared libs on, rnp shared libs on	2m 55s
package-source	29s
system-sexpp, sexpp shared libs on, rnp shared libs off	2m 47s
ubuntu-latest [CC gcc; botan; shared libs on; GnuPG stable]	4m 13s
system-sexpp, sexpp shared libs off, rnp shared libs on	3m 3s
ubuntu-latest [CC clang; botan; shared libs on; GnuPG stable]	4m 7s
system-sexpp, sexpp shared libs off, rnp shared libs off	2m 48s
ubuntu-latest [CC gcc; openssl; shared libs on; GnuPG stable]	4m 13s
ubuntu-latest [CC clang; openssl; shared libs on; GnuPG stable]	4m 11s
ubuntu-20.04 [CC gcc; openssl; shared libs on; GnuPG stable]	3m 34s
ubuntu-latest [CC gcc; botan; shared libs off; GnuPG stable]	4m 20s
package	50s
debian-tests	12s
	45m 56s

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