[CI] Switch to Ubuntu 26.04 (#827) #5040

Job	Run time
ci-scope	3s
pre-commit / link-check	44s
pre-commit / pre-commit	2m 10s
ubuntu / clang-build (ubuntu-26.04)	2m 44s
ubuntu / gcc-build (ubuntu-26.04, Debug)	2m 16s
ubuntu / gcc-build (ubuntu-26.04, Release)	2m 14s
mac / clang-build (Debug)	3m 21s
windows / clang-build	2m 34s
mac / clang-build (Release)	2m 14s
windows / msvc-build (Release)	2m 17s
windows / msvc-build (Debug)	3m 22s
ubuntu / gcc-test (ubuntu-26.04)	2m 59s
windows / clang-test	1m 33s
ubuntu / clang-sanitizer-build (ubuntu-26.04)	3m 50s
ubuntu / clang-test (ubuntu-26.04)	2m 37s
mac / clang-test	1m 29s
windows / msvc-test	2m 28s
windows / clang-test-extended	1m 44s
mac / clang-test-extended	1m 23s
ubuntu / gcc-test-extended (ubuntu-26.04)	1m 34s
ubuntu / clang-test-extended (ubuntu-26.04)	1m 54s
windows / msvc-test-extended	1m 34s
ubuntu / clang-sanitizer-test (ubuntu-26.04)	1m 3s
ubuntu / gcc-build-codecov	4m 19s
ubuntu / clang-sanitizer-test-extended (ubuntu-26.04)	1m 4s
perf / macos-clang-build-perf-stats	1m 43s
perf / ubuntu-gcc-build-perf-stats	1m 14s
pages / build-doxygen-xml	13s
pages / build-scoreboard	20s
pages / build-sphinx	39s
pages / deploy-pages	-1s
	57m 38s

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