mage: run mage update steps in parallel (#6871)

From the looks of it, none of the update steps interact with each other, so
I don't see a reason to run them serially.

As an example, making a single line change in the otel components file results
in the following timings:

	parallel mage update  9.19s user 1.92s system 366% cpu 3.027 total
	serial mage update  20.20s user 2.93s system 181% cpu 12.748 total

magefile.go

@@ -651,7 +651,7 @@ func commitID() string {
 
 // Update is an alias for executing control protocol, configs, and specs.
 func Update() {
-	mg.SerialDeps(Config, BuildPGP, BuildFleetCfg, Otel.Readme)
+	mg.Deps(Config, BuildPGP, BuildFleetCfg, Otel.Readme)
 }
 
 func EnsureCrossBuildOutputDir() error {