runtime: enable the exectracer2 experiment by default

Fixes #60773.

Cq-Include-Trybots: luci.golang.try:gotip-linux-amd64-longtest,gotip-linux-amd64-longtest-race
Change-Id: Ice3fd4577d58ce593611144242f2cba99c9d2ecb
Reviewed-on: https://go-review.googlesource.com/c/go/+/540778
LUCI-TryBot-Result: Go LUCI <golang-scoped@luci-project-accounts.iam.gserviceaccount.com>
Reviewed-by: Michael Pratt <mpratt@google.com>
Auto-Submit: Michael Knyszek <mknyszek@google.com>

src/internal/buildcfg/exp.go

@@ -74,6 +74,7 @@ func ParseGOEXPERIMENT(goos, goarch, goexp string) (*ExperimentFlags, error) {
 		RegabiArgs:       regabiSupported,
 		CoverageRedesign: true,
 		AllocHeaders:     true,
+		ExecTracer2:      true,
 	}
 
 	// Start with the statically enabled set of experiments.