test: Add latest versions for v1.13, v1.14, and v1.15 (alpha). Replace use of `Latest_Alpha_v1_10`.

tfexec/internal/e2etest/init_test.go

diff --git a/tfexec/internal/e2etest/init_test.go b/tfexec/internal/e2etest/init_test.go
index 896e72f..0be533f 100644
--- a/tfexec/internal/e2etest/init_test.go
+++ b/tfexec/internal/e2etest/init_test.go
@@ -52,8 +52,7 @@
 func TestInitJSON_TF19AndLater(t *testing.T) {
 	versions := []string{
 		testutil.Latest_v1_9,
-		testutil.Latest_Alpha_v1_9,
-		testutil.Latest_Alpha_v1_10,
+		testutil.Latest_v1_10,
 	}
 
 	runTestWithVersions(t, versions, "basic", func(t *testing.T, tfv *version.Version, tf *tfexec.Terraform) {

tfexec/internal/testutil/tfcache.go

diff --git a/tfexec/internal/testutil/tfcache.go b/tfexec/internal/testutil/tfcache.go
index fa7d260..abb8465 100644
--- a/tfexec/internal/testutil/tfcache.go
+++ b/tfexec/internal/testutil/tfcache.go
@@ -29,14 +29,18 @@
 	Latest_v1_6        = "1.6.6"
 	Latest_v1_7        = "1.7.5"
 	Latest_v1_8        = "1.8.5"
-	Latest_Beta_v1_8   = "1.8.0-beta1"
 	Latest_v1_9        = "1.9.8"
-	Latest_Alpha_v1_9  = "1.9.0-alpha20240516"
 	Latest_v1_10       = "1.10.5"
-	Latest_Alpha_v1_10 = "1.10.0-alpha20240926"
 	Latest_v1_11       = "1.11.4"
 	Latest_v1_12       = "1.12.2"
+	Latest_v1_13       = "1.13.5"
+	Latest_v1_14       = "1.14.3"
 	Latest_Alpha_v1_14 = "1.14.0-alpha20250903"
+	Latest_Alpha_v1_15 = "1.15.0-alpha20251203"
+
+	// Special cases
+	Latest_Beta_v1_8  = "1.8.0-beta1"         // Used to test experiments are disabled in betas
+	Latest_Alpha_v1_9 = "1.9.0-alpha20240516" // Used to test deferred actions and that experiments are enabled in actions
 )
 
 const appendUserAgent = "tfexec-testutil"