Update GCC version #2432

Job	Run time
build (gcc-15.deb, --std-tests)	6m 4s
build_system	25s
build (gcc-15.deb, --test-libcore)	14m 42s
build (gcc-15.deb, --extended-rand-tests)	8m 16s
build (gcc-15.deb, --extended-regex-example-tests)	6m 46s
duplicates	4s
build (gcc-15.deb, --extended-regex-tests)	12m 17s
build (gcc-15.deb, --test-successful-rustc --nb-parts 2 --current-part 0)	11m 18s
build (gcc-15.deb, --test-successful-rustc --nb-parts 2 --current-part 1)	11m 45s
build (gcc-15.deb, --projects)	11m 17s
build (gcc-15-without-int128.deb, --std-tests)	6m 21s
build (gcc-15-without-int128.deb, --test-libcore)	14m 37s
build (gcc-15-without-int128.deb, --extended-rand-tests)	8m 50s
build (gcc-15-without-int128.deb, --extended-regex-example-tests)	6m 24s
build (gcc-15-without-int128.deb, --extended-regex-tests)	11m 33s
build (gcc-15-without-int128.deb, --test-successful-rustc --nb-parts 2 --current-part 0)	11m 21s
build (gcc-15-without-int128.deb, --test-successful-rustc --nb-parts 2 --current-part 1)	11m 30s
build (gcc-15-without-int128.deb, --projects)	11m 55s
	2h 45m 25s

Provide feedback