Auto merge of #33934 - Byron:libsyntex-ring-buffer-size, r=pnkfelix

Prevent overflows by increasing ring buffer size

Please note that this change is just done to prevent
issues as currently seen by syntex_syntax in future.
See https://github.com/serde-rs/syntex/pull/47 for details.

As shown in https://github.com/serde-rs/syntex/issues/33,
complex code can easily overflow the ring-buffer and
cause an assertion error.