Pin Terraform binary version to 1.5.5 (#715)

## Changes

The installer doesn't respect the version constraints if they are
specified.

Source: [the vc argument is not
used](https://github.com/hashicorp/hc-install/blob/850464c6016513fc7ad47114d010080ec16f32cb/releases/latest_version.go#L158-L177).

## Tests

Confirmed manually.

bundle/deploy/terraform/init.go

@@ -55,10 +55,10 @@ func (m *initialize) findExecPath(ctx context.Context, b *bundle.Bundle, tf *con
 	}
 
 	// Download Terraform to private bin directory.
-	installer := &releases.LatestVersion{
-		Product:     product.Terraform,
-		Constraints: version.MustConstraints(version.NewConstraint("<=1.5.5")),
-		InstallDir:  binDir,
+	installer := &releases.ExactVersion{
+		Product:    product.Terraform,
+		Version:    version.Must(version.NewVersion("1.5.5")),
+		InstallDir: binDir,
 	}
 	execPath, err = installer.Install(ctx)
 	if err != nil {