Update GitHub Actions workflows. (#529)

This PR was automatically generated by the
update-workflows-ecosystem-providers workflow in the pulumi/ci-mgmt
repo, from commit d7c62aa3eaa24dc23f8ef7b72eb075da9fcb07e2.

Author: pulumi-bot

Makefile

@@ -163,7 +163,7 @@ tfgen_build_only:
 
 upstream:
 ifneq ("$(wildcard upstream)","")
-	./upstream.sh init
+	./upstream.sh init -f
 endif
 
 bin/pulumi-java-gen: .pulumi-java-gen.version

upstream.sh

@@ -97,7 +97,7 @@ Either stage or reset the 'upstream' submodule changes before continuing:
 
     git add upstream
     # or #
-    git checkout upstream
+    (cd upstream && git checkout <current submodule commit of origin/default> && cd -)
 
 EOF
     exit 1