docs(benchmarks): remove em dashes from interning writeup

docs/benchmarks.md

@@ -151,11 +151,11 @@ patched.
   each repeated 100k times), interning gated to fire only above the
   small-string threshold. Result (two interleaved A/B pairs each, XSTS clean):
   neutral-to-slightly-negative on short names, and **decisively NEGATIVE on
-  long names, ~4-5% slower, both pairs** — the opposite of the hypothesis.
+  long names, ~4-5% slower, both pairs**: the opposite of the hypothesis.
   The complete mechanism, which the boundary test forced out: a Swift
   `String` is reference-counted, so interning does not merely avoid an
   allocation, it trades that allocation for **ARC traffic on the shared
-  instance** — every cache probe copies a `String` out of a slot (a retain),
+  instance**: every cache probe copies a `String` out of a slot (a retain),
   and a hit returns another retain. For the name sizes that occur in XML,
   the atomic retain/release traffic to share one heap `String` costs more
   than the small `malloc` + memcpy + UTF-8 validation it was meant to