Invalid JSON errot with `act push` locally

[cburroughs]

I am new to act but was able to run the demos from https://github.com/cplee/github-actions-demo In this repo, when I try to run act push as suggested in the readme I get:

$ act push
INFO[0000] Using docker host 'unix:///var/run/docker.sock', and daemon socket 'unix:///var/run/docker.sock' 
[Build and Release protoc-gen-grpc-python/prepare] 🚧  Skipping unsupported platform -- Try running with `-P ubuntu-24.04=...`
ERRO[0000] Error while evaluating matrix: Invalid JSON: invalid character '$' looking for beginning of value 

If I run with -v the preceding lines are:

DEBU[0000] evaluating expression '${{ fromJson(needs.prepare.outputs.matrix) }}' 
DEBU[0000] expression '${{ fromJson(needs.prepare.outputs.matrix) }}' evaluated to '%!t(<nil>)' 
ERRO[0000] Error while evaluating matrix: Invalid JSON: invalid character '$' looking for beginning of value 

$ act --bug-report
act version:            0.2.82
GOOS:                   linux
GOARCH:                 amd64
NumCPU:                 16
Docker host:            DOCKER_HOST environment variable is not set
Sockets found:
	/var/run/docker.sock
Config files:           
	/home/ecsb/.config/act/actrc:
		-P ubuntu-latest=catthehacker/ubuntu:act-latest
		-P ubuntu-22.04=catthehacker/ubuntu:act-22.04
		-P ubuntu-20.04=catthehacker/ubuntu:act-20.04
		-P ubuntu-18.04=catthehacker/ubuntu:act-18.04
	.actrc:
		-P ubuntu-latest=catthehacker/ubuntu:act-latest
		-P ubuntu-22.04=catthehacker/ubuntu:act-22.04
		-P ubuntu-20.04=catthehacker/ubuntu:act-20.04
		
		# Use GitHub runners for macOS (requires GitHub runners or skip)
		-P macos-latest=catthehacker/ubuntu:act-latest
		-P macos-13=catthehacker/ubuntu:act-latest
		
		# Windows (limited support in act)
		-P windows-latest=catthehacker/ubuntu:act-latest
		
		# Environment variables for testing
		--env GITHUB_TOKEN=dummy_token_for_testing
		
		# Skip jobs that require secrets by default
		# Remove this line if you want to test with real secrets
		--job build
Build info:
	Go version:            go1.24.0
	Module path:           github.com/nektos/act
	Main version:          v0.2.82
	Main path:             github.com/nektos/act
	Main checksum:         
	Build settings:
		-buildmode:           exe
		-compiler:            gc
		-ldflags:             -s -w -X main.version=0.2.82 -X main.commit=3d71542867d7cbdac6a75e540be6f64362e94de2 -X main.date=2025-10-01T02:36:39Z -X main.builtBy=goreleaser
		CGO_ENABLED:          0
		GOARCH:               amd64
		GOOS:                 linux
		GOAMD64:              v1
		vcs:                  git
		vcs.revision:         3d71542867d7cbdac6a75e540be6f64362e94de2
		vcs.time:             2025-10-01T02:36:13Z
		vcs.modified:         false
Docker Engine:
	Engine version:        28.0.4
	Engine runtime:        runc
	Cgroup version:        2
	Cgroup driver:         cgroupfs
	Storage driver:        overlayfs
	Registry URI:          https://index.docker.io/v1/
	OS:                    Gentoo Linux
	OS type:               linux
	OS version:            2.18
	OS arch:               x86_64
	OS kernel:             6.12.47-gentoo-dist
	OS CPU:                16
	OS memory:             62077 MB
	Security options:
		name=seccomp,profile=builtin
		name=cgroupns