Stdin::read_line: read_line does not need a mutable borrow

[RalfJung]

This fixes #26890.

To be honest, the local compile-test is still running. This just takes so long. But this looks trivial enough...

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[alexcrichton]

Tagging with T-libs and I-needs-decision to ensure this comes up during triage

[RalfJung]

It locally compiles and passes libstd tests.

[RalfJung]

Any news on this? Just trying to make sure this one doesn't get lost :)

[alexcrichton]

@RalfJung yes sorry this past triage meeting was quite busy with agenda items, but I think we'll be able to get to this this week!

[alexcrichton]

Ok we talked about this at the libs triage meeting today and the decision was to move forward with this, but to ensure we don't have unexpected breakage I'm going to run crater first.

[alexcrichton]

This has zero regressions on crater, so I'm going to r+, thanks @RalfJung!

@bors: r+ 24f21f2

[bors]

⌛ Testing commit 24f21f2 with merge dc966ef...

[bors]

☀️ Test successful - auto-linux-32-nopt-t, auto-linux-32-opt, auto-linux-64-nopt-t, auto-linux-64-opt, auto-linux-64-x-android-t, auto-mac-32-opt, auto-mac-64-nopt-t, auto-mac-64-opt, auto-win-gnu-32-nopt-t, auto-win-gnu-32-opt, auto-win-gnu-64-nopt-t, auto-win-gnu-64-opt, auto-win-msvc-32-opt, auto-win-msvc-64-opt