Fix soundness problem when matching `iso` variables #2872

Job	Run time
Lint bash, docker, markdown, and yaml	1m 45s
Lint bash, docker, markdown, and yaml	1m 45s
Validate musl Docker image builds	18s
Validate musl Docker image builds	18s
Validate GNU Docker image builds	31s
Validate GNU Docker image builds	31s
Validate GNU Docker release image builds	33s
Validate GNU Docker release image builds	33s
riscv64 Linux glibc	23m 36s
riscv64 Linux glibc	23m 36s
Validate musl Docker release image builds	19s
Validate musl Docker release image builds	19s
Validate Windows Docker release image builds	7m 3s
Validate Windows Docker release image builds	7m 3s
Verify CHANGELOG is valid	4s
Verify CHANGELOG is valid	4s
aarch64 Linux glibc	18m 25s
aarch64 Linux glibc	18m 25s
arm64 Apple Darwin	14m 57s
arm64 Apple Darwin	14m 57s
armhf Linux glibc	28m 15s
armhf Linux glibc	28m 15s
arm Linux glibc	28m 32s
arm Linux glibc	28m 32s
Validate Windows Docker image builds	10m 38s
Validate Windows Docker image builds	10m 38s
x86-64 Linux glibc	22m 27s
x86-64 Linux glibc	22m 27s
x86-64 Apple Darwin	31m 31s
x86-64 Apple Darwin	31m 31s
x86-64 Linux musl	24m 35s
x86-64 Linux musl	24m 35s
x86-64 Windows MSVC	36m 58s
x86-64 Windows MSVC	36m 58s
use dtrace	20m 51s
use dtrace	20m 51s
use pool_memalign	6m 2s
use pool_memalign	26m 26s
use runtimestats	22m 2s
use runtimestats	22m 2s
	10h 19m 8s

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