CI: Update FreeBSD image version for Cirrus runner. #3312

Job	Run time
ubuntu-latest [CC gcc; botan; shared libs on; GnuPG stable]	4m 0s
cmake-offline-googletest-src	4m 17s
ubuntu-latest [CC clang; botan; shared libs on; GnuPG stable]	4m 27s
ubuntu-latest [CC gcc; openssl; shared libs on; GnuPG stable]	4m 19s
cmake-offline-googletest	4m 7s
ubuntu-latest [CC clang; openssl; shared libs on; GnuPG stable]	4m 11s
system-sexpp, sexpp shared libs on, rnp shared libs on	2m 48s
ubuntu-20.04 [CC gcc; openssl; shared libs on; GnuPG stable]	3m 43s
system-sexpp, sexpp shared libs on, rnp shared libs off	2m 59s
ubuntu-latest [CC gcc; botan; shared libs off; GnuPG stable]	4m 3s
system-sexpp, sexpp shared libs off, rnp shared libs on	2m 44s
system-sexpp, sexpp shared libs off, rnp shared libs off	2m 42s
package-source	27s
package	51s
debian-tests	9s
	45m 47s

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