Fix wrong mirror URL of bazel-toolchains 3.1.0.
Fix wrong mirror URL of bazel-toolchains 3.1.0.

RELNOTES: None.
PiperOrigin-RevId: 313771454

bazelbuild/bazel,ulfjack/bazel,safarmer/bazel,meteorcloudy/bazel,ulfjack/bazel,ButterflyNetwork/bazel,katre/bazel,bazelbuild/bazel,meteorcloudy/bazel,katre/bazel,werkt/bazel,safarmer/bazel,ButterflyNetwork/bazel,ulfjack/bazel,werkt/bazel,meteorcloudy/bazel,werkt/bazel,ButterflyNetwork/bazel,twitter-forks/bazel,perezd/bazel,davidzchen/bazel,cushon/bazel,werkt/bazel,twitter-forks/bazel,meteorcloudy/bazel,katre/bazel,safarmer/bazel,perezd/bazel,perezd/bazel,meteorcloudy/bazel,bazelbuild/bazel,ulfjack/bazel,katre/bazel,werkt/bazel,ButterflyNetwork/bazel,katre/bazel,ulfjack/bazel,werkt/bazel,perezd/bazel,bazelbuild/bazel,ButterflyNetwork/bazel,twitter-forks/bazel,ButterflyNetwork/bazel,safarmer/bazel,meteorcloudy/bazel,cushon/bazel,cushon/bazel,perezd/bazel,davidzchen/bazel,davidzchen/bazel,katre/bazel,bazelbuild/bazel,ulfjack/bazel,perezd/bazel,bazelbuild/bazel,davidzchen/bazel,cushon/bazel,twitter-forks/bazel,davidzchen/bazel,perezd/bazel,ulfjack/bazel,meteorcloudy/bazel,davidzchen/bazel,safarmer/bazel,safarmer/bazel,cushon/bazel,twitter-forks/bazel,cushon/bazel,twitter-forks/bazel,davidzchen/bazel,twitter-forks/bazel