net: do not modify shared test variable in TestDNSReadConfig
net: do not modify shared test variable in TestDNSReadConfig

Fixes #56542

Change-Id: I294856f8fb4d49393310ec92ab40fb7d841b6570
GitHub-Last-Rev: a4563400af816caa6119775b7b01b51134c62149
GitHub-Pull-Request: golang/go#56545
Reviewed-on: https://go-review.googlesource.com/c/go/+/447198
Reviewed-by: Bryan Mills <1c8aad60184261ccede67f5c63a0d2a3bf3c9ff4@google.com>
Run-TryBot: Bryan Mills <1c8aad60184261ccede67f5c63a0d2a3bf3c9ff4@google.com>
Auto-Submit: Bryan Mills <1c8aad60184261ccede67f5c63a0d2a3bf3c9ff4@google.com>
Reviewed-by: Matthew Dempsky <e56ac2c500064424afac424d4b5e53bd0570a731@google.com>
TryBot-Result: Gopher Robot <66cb808b70d30c07676d5e946fee83fd561249e5@golang.org>

golang/go,golang/go,golang/go,golang/go,golang/go,golang/go,golang/go,golang/go