Update sexpp reference to v0.9.0 #3736

Job	Run time
cmake-offline-googletest	4m 7s
cmake-offline-googletest-src	4m 16s
system-sexpp, sexpp shared libs on, rnp shared libs on	2m 53s
system-sexpp, sexpp shared libs on, rnp shared libs off	2m 52s
package-source	29s
system-sexpp, sexpp shared libs off, rnp shared libs on	2m 46s
ubuntu-latest [CC gcc; botan; shared libs on; GnuPG stable]	4m 21s
ubuntu-latest [CC clang; botan; shared libs on; GnuPG stable]	4m 30s
system-sexpp, sexpp shared libs off, rnp shared libs off	2m 53s
ubuntu-latest [CC gcc; openssl; shared libs on; GnuPG stable]	4m 11s
ubuntu-latest [CC clang; openssl; shared libs on; GnuPG stable]	4m 1s
ubuntu-20.04 [CC gcc; openssl; shared libs on; GnuPG stable]	3m 42s
ubuntu-latest [CC gcc; botan; shared libs off; GnuPG stable]	5m 2s
package	1m 1s
debian-tests	10s
	47m 14s

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