CI: remove support for ubuntu-20.04 #5087

Job	Run time
Python Bindings (ubuntu-latest)	1m 18s
ubuntu-22.04 --with-local-libgcrypt cc	4m 57s
LTO and Gold Linker gcc-14	3m 34s
LTO and Gold Linker clang-18	2m 35s
ubuntu-22.04 cc	5m 0s
Test Utils (ubuntu-latest)	2m 38s
ubuntu-24.04 --with-local-libgcrypt cc	8m 7s
ubuntu-24.04 cc	8m 3s
macOS-13 --with-local-libgcrypt cc	4m 22s
windows-latest (msys2) --with-local-libgcrypt	7m 7s
macOS-13 cc	4m 36s
windows-latest (msys2)	7m 2s
macOS-14 --with-local-libgcrypt cc	3m 1s
macOS-14 cc	2m 29s
macOS-15 --with-local-libgcrypt cc	2m 28s
macOS-15 cc	2m 17s
ubuntu-22.04-arm --with-local-libgcrypt cc	2m 22s
ubuntu-22.04-arm cc	2m 29s
ubuntu-24.04-arm --with-local-libgcrypt cc	2m 51s
ubuntu-24.04-arm cc	2m 58s
ubuntu-22.04 gcc-4.9 --with-pcre2 --with-maxminddb --with-sanitizer	9m 0s
ubuntu-24.04 gcc-14 --with-pcre2 --with-maxminddb --with-sanitizer	12m 43s
ubuntu-22.04 clang-12 --with-pcre2 --with-maxminddb --with-sanitizer	13m 46s
ubuntu-24.04 clang-18 --with-pcre2 --with-maxminddb --with-sanitizer	14m 57s
ubuntu-latest cc --with-pcre2 --with-maxminddb nBPF	5m 50s
ubuntu-latest cc --with-pcre2 --with-maxminddb --disable-global-context-support	5m 26s
macOS-latest cc --with-pcre2 --with-maxminddb	3m 2s
	2h 24m 58s

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