CI: Update FreeBSD image version for Cirrus runner. #3318

Job	Run time
cmake-offline-googletest	4m 39s
cmake-offline-googletest-src	4m 3s
system-sexpp, sexpp shared libs on, rnp shared libs on	3m 3s
package-source	31s
system-sexpp, sexpp shared libs on, rnp shared libs off	2m 56s
system-sexpp, sexpp shared libs off, rnp shared libs on	2m 55s
system-sexpp, sexpp shared libs off, rnp shared libs off	2m 55s
ubuntu-latest [CC gcc; botan; shared libs on; GnuPG stable]	4m 16s
ubuntu-latest [CC clang; botan; shared libs on; GnuPG stable]	4m 27s
ubuntu-latest [CC gcc; openssl; shared libs on; GnuPG stable]	5m 5s
ubuntu-latest [CC clang; openssl; shared libs on; GnuPG stable]	4m 14s
ubuntu-20.04 [CC gcc; openssl; shared libs on; GnuPG stable]	4m 0s
ubuntu-latest [CC gcc; botan; shared libs off; GnuPG stable]	4m 10s
package	56s
debian-tests	32s
	48m 42s

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