Remove tests, sexpp and certain code lines from the Coverage report. #3486

Job	Run time
ubuntu-latest [CC gcc; botan; shared libs on; GnuPG stable]	4m 13s
ubuntu-latest [CC clang; botan; shared libs on; GnuPG stable]	4m 16s
ubuntu-latest [CC gcc; openssl; shared libs on; GnuPG stable]	4m 3s
ubuntu-latest [CC clang; openssl; shared libs on; GnuPG stable]	4m 12s
ubuntu-20.04 [CC gcc; openssl; shared libs on; GnuPG stable]	3m 41s
ubuntu-latest [CC gcc; botan; shared libs off; GnuPG stable]	4m 23s
cmake-offline-googletest-src	4m 20s
cmake-offline-googletest	4m 22s
system-sexpp, sexpp shared libs on, rnp shared libs on	2m 52s
package-source	31s
system-sexpp, sexpp shared libs on, rnp shared libs off	2m 53s
system-sexpp, sexpp shared libs off, rnp shared libs on	2m 55s
system-sexpp, sexpp shared libs off, rnp shared libs off	2m 54s
package	1s
debian-tests	1s
	45m 37s

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