Added `slackb.com` SNI. #2882

Job	Run time
Python Bindings (ubuntu-latest)	1m 24s
Test Utils (ubuntu-latest)	2m 3s
ubuntu-latest x86_64 --with-local-libgcrypt cc	9m 23s
ubuntu-latest x86_64 cc	8m 59s
ubuntu-20.04 x86_64 --with-local-libgcrypt cc	9m 40s
ubuntu-20.04 x86_64 cc	9m 1s
macOS-latest x86_64 --with-local-libgcrypt cc	6m 27s
macOS-latest x86_64 cc	6m 4s
macos-11 x86_64 --with-local-libgcrypt cc	6m 54s
macos-11 x86_64 cc	6m 52s
windows-latest x86_64 --with-local-libgcrypt cc	21m 41s
windows-latest x86_64 cc	12m 42s
ubuntu-20.04 x86_64 gcc-7 --with-pcre --with-maxminddb --with-sanitizer	21m 30s
ubuntu-22.04 x86_64 gcc-12 --with-pcre --with-maxminddb --with-sanitizer --with-lto-and-gold-linker	21m 5s
ubuntu-20.04 x86_64 clang-7 --with-pcre --with-maxminddb --with-sanitizer	24m 2s
ubuntu-22.04 x86_64 clang-14 --with-pcre --with-maxminddb --with-sanitizer --with-lto-and-gold-linker	29m 45s
ubuntu-latest x86_64 cc --with-pcre --with-maxminddb --with-thread-sanitizer	53m 29s
ubuntu-latest x86_64 cc --with-pcre --with-maxminddb --with-sanitizer nBPF	22m 22s
ubuntu-22.04 x86_64 clang-14 --with-pcre --with-maxminddb --with-memory-sanitizer	1h 7m 31s
macOS-latest x86_64 cc --with-pcre --with-maxminddb	6m 44s
macos-12 x86_64 cc --with-pcre --with-maxminddb	7m 42s
ubuntu-latest arm64 cc --with-pcre --with-maxminddb	34m 16s
ubuntu-latest armhf cc --with-pcre --with-maxminddb --with-sanitizer	1h 42m 49s
ubuntu-latest s390x cc --with-pcre --with-maxminddb	41m 53s
	8h 54m 18s

Provide feedback