runtime: allocation in printfloat64 causes throw [1.26 backport]

[gopherbot]

@prattmic requested issue #77854 to be considered for backport to the next 1.26 minor release.

@gopherbot please backport to 1.26. This is a regression that can cause random crashes when using GODEBUG=gcpacertrace=1, and likely other modes that print in the runtime.

[gopherbot]

Change https://go.dev/cl/750760 mentions this issue: [release-branch.go1.26] runtime: fix printfloat, printcomplex buffer sizes