Read release info from build info

Since go1.18, vcs.revision gets compiled into the binary and can be
read.

Conveniently, debug.ReadBuildInfo has been around since go1.12, so
there's no need to conditionally compile this unless sentry-go needs to
support < go1.12 for some reason.

So in builds newer than 1.18, this key just simply won't exist and
effectively will do nothing.

This is much more convenient to detect in anything go1.18 since it's
much more common to have this compiled in.

util.go

@@ -6,6 +6,7 @@ import (
 	"encoding/json"
 	"fmt"
 	"os"
+	"runtime/debug"
 	"strings"
 	"time"
 
@@ -66,6 +67,15 @@ func defaultRelease() (release string) {
 		}
 	}
 
+	if info, ok := debug.ReadBuildInfo(); ok {
+		for _, setting := range info.Settings {
+			if setting.Key == "vcs.revision" && setting.Value != "" {
+				Logger.Printf("Using release from debug info: %s", setting.Value)
+				return setting.Value
+			}
+		}
+	}
+
 	// Derive a version string from Git. Example outputs:
 	// 	v1.0.1-0-g9de4
 	// 	v2.0-8-g77df-dirty