Reduce test phase for constant time left shift #640

Job	Run time
Sanitizers (sanitizer, msvc, windows-2022, ninja)	22m 47s
Cross (cross-alpha, gcc, ubuntu-24.04)	6m 3s
Sanitizers (sanitizer, gcc, ubuntu-24.04)	37m 0s
clang-tidy	1h 17m 21s
Cross (cross-hppa64, gcc, ubuntu-24.04)	24m 1s
Cross (cross-m68k, gcc, ubuntu-24.04)	18m 33s
PQ/T TLS 1.3	47s
Cross (cross-mips, gcc, ubuntu-24.04)	12m 5s
TLS-Anvil (server)	31m 29s
Cross (cross-ppc32, gcc, ubuntu-24.04)	43s
Cross (cross-sh4, gcc, ubuntu-24.04)	15m 37s
valgrind	1h 26m 5s
Cross (cross-sparc64, gcc, ubuntu-24.04)	21m 48s
Cross (cross-riscv64, gcc, ubuntu-24.04)	7m 58s
Cross (cross-s390x, gcc, ubuntu-24.04)	16m 8s
Cross (cross-android-arm64-amalgamation, clang, ubuntu-24.04)	54s
Cross (cross-arm64-amalgamation, gcc, ubuntu-24.04)	11m 20s
Cross (emscripten, emcc, macos-14)	55m 39s
Cross (sde, gcc, ubuntu-24.04)	13m 35s
	7h 39m 53s

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