go.mod: Remove `toolchain` directive (#622)

go.mod

diff --git a/go.mod b/go.mod
index 5c4b8b5..8f503a4 100644
--- a/go.mod
+++ b/go.mod
@@ -1,10 +1,8 @@
 module github.com/hashicorp/terraform-exec
 
-// Keep last digit at zero, use toolchain for Go build requirement
+// Keep last digit at zero, do not use toolchain directive (this is a library)
 go 1.26.0
 
-toolchain go1.26.8
-
 require (
 	github.com/google/go-cmp v0.7.0
 	github.com/hashicorp/go-version v1.9.0