Fix blanket "unexpected assign token" error message / usability issue #10272

Job	Run time
Go Lint	1m 34s
Generate Code	1m 6s
Rego PR checks	1m 30s
YAML Lint	15s
Check Generated	23s
Go compat build/test (ubuntu-22.04, 1.20)	4m 5s
Go Test (linux)	4m 29s
Go Build (linux amd64)	2m 40s
Go compat build/test (macos-14, 1.20)	4m 35s
Go Test (darwin)	3m 56s
Go Race Detector	6m 5s
Go Build (linux arm64)	2m 3s
Go Build (linux arm64GO_TAGS="-tags=opa_no_oci")	2m 3s
WASM	5m 33s
Go Build (windows amd64)	2m 23s
Go Build (darwin amd64)	1m 55s
Go Build (darwin arm64)	54s
docker image smoke test	28s
smoke-test-binaries (linux, ubuntu-22.04, opa_linux_amd64, amd64)	11s
smoke-test-binaries (linux, ubuntu-22.04, opa_linux_amd64_static, amd64, disabled)	9s
smoke-test-binaries (darwin, macos-13, opa_darwin_amd64, amd64)	26s
smoke-test-binaries (darwin, macos-14, opa_darwin_arm64_static, arm64, disabled)	15s
smoke-test-binaries (windows, windows-latest, opa_windows_amd64.exe, amd64)	43s
	47m 41s

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