fix: revert go mod compat for sdk,api to 1.19 (#16323) (#16327)

Co-authored-by: Dan Stough <dan.stough@hashicorp.com>

api/go.mod

@@ -1,6 +1,6 @@
 module github.com/hashicorp/consul/api
 
-go 1.20
+go 1.19
 
 replace github.com/hashicorp/consul/sdk => ../sdk
 

sdk/freeport/freeport.go

@@ -76,6 +76,9 @@ var (
 	// total is the total number of available ports in the block for use.
 	total int
 
+	// seededRand is a random generator that is pre-seeded from the current time.
+	seededRand *rand.Rand
+
 	// stopCh is used to signal to background goroutines to terminate. Only
 	// really exists for the safety of reset() during unit tests.
 	stopCh chan struct{}
@@ -114,6 +117,7 @@ func initialize() {
 		panic("freeport: block size too big or too many blocks requested")
 	}
 
+	seededRand = rand.New(rand.NewSource(time.Now().UnixNano())) // This is compatible with go 1.19 but unnecessary in >= go1.20
 	firstPort, lockLn = alloc()
 
 	condNotEmpty = sync.NewCond(&mu)
@@ -255,7 +259,7 @@ func adjustMaxBlocks() (int, error) {
 // be automatically released when the application terminates.
 func alloc() (int, net.Listener) {
 	for i := 0; i < attempts; i++ {
-		block := int(rand.Int31n(int32(effectiveMaxBlocks)))
+		block := int(seededRand.Int31n(int32(effectiveMaxBlocks)))
 		firstPort := lowPort + block*blockSize
 		ln, err := net.ListenTCP("tcp", tcpAddr("127.0.0.1", firstPort))
 		if err != nil {

sdk/go.mod

@@ -1,6 +1,6 @@
 module github.com/hashicorp/consul/sdk
 
-go 1.20
+go 1.19
 
 require (
 	github.com/hashicorp/go-cleanhttp v0.5.1