all: fix spelling

Change-Id: I68538a50c22b02cdb5aa2a889f9440fed7b94c54
GitHub-Last-Rev: aaac9e7834
GitHub-Pull-Request: golang/go#52944
Reviewed-on: https://go-review.googlesource.com/c/go/+/406835
Reviewed-by: Bryan Mills <bcmills@google.com>
Reviewed-by: Robert Griesemer <gri@google.com>
TryBot-Result: Gopher Robot <gobot@golang.org>
Run-TryBot: Bryan Mills <bcmills@google.com>
Auto-Submit: Bryan Mills <bcmills@google.com>

test/live_uintptrkeepalive.go

@@ -12,7 +12,7 @@
 // bodies (assembly, linkname), as well as explicitly on complete functions
 // with //go:uintptrkeepalive.
 //
-// This is most important for syscall.Syscall (and similiar functions), so we
+// This is most important for syscall.Syscall (and similar functions), so we
 // test it explicitly.
 
 package p