Update GitHub Actions workflows. (#279)

This PR was automatically generated by the
update-workflows-ecosystem-providers workflow in the pulumi/ci-mgmt
repo, from commit 601cb710ba9f79f930d32c37262a5747abb135ed.

Makefile

@@ -150,7 +150,7 @@ ci-mgmt: .ci-mgmt.yaml
 		--config $<
 
 .pulumi/bin/pulumi: .pulumi/version
-	curl -fsSL https://get.pulumi.com | HOME=$(WORKING_DIR) sh -s -- --version $(cat .pulumi/version)
+	curl -fsSL https://get.pulumi.com | HOME=$(WORKING_DIR) sh -s -- --version $(shell cat .pulumi/version)
 
 # Compute the version of Pulumi to use by inspecting the Go dependencies of the provider.
 .pulumi/version: