Make `parse_policy_or_template_to_est` error for CST that aren't valid AST #2068

	name: Cargo Build & Test

	on:
	pull_request:

	env:
	CARGO_TERM_COLOR: always
	jobs:
	build_and_test:
	uses: ./.github/workflows/build_and_test.yml

	cargo_semver_checks:
	name: Cargo SemVer Checks
	runs-on: ubuntu-latest
	# Make this check mandatory for release branches.
	continue-on-error: ${{ !startsWith(github.base_ref, 'release/') }}
	strategy:
	matrix:
	toolchain:
	- stable
	steps:
	- name: Check out head (${{ github.head_ref }})
	uses: actions/checkout@v4
	with:
	path: head
	# Pull requests to non-release branches are checked for SemVer breakage
	# relative to their target branch.
	- if: ${{ !startsWith(github.base_ref, 'release/') }}
	name: Check out base (${{ github.base_ref }})
	uses: actions/checkout@v4
	with:
	ref: ${{ github.base_ref }}
	path: base
	# If this is a release PR, check SemVer relative to the highest version
	# published to crates.io <= the version from head.
	- if: ${{ startsWith(github.base_ref, 'release/') }}
	name: Check out base (from crates.io)
	run: head/.github/scripts/check-out-base-from-crates-io.sh
	shell: bash
	# `cargo semver-checks` doesn't understand `rlib` crates.
	- run: >-
	sed -i -E 's/^(crate-type = \["rlib", "cdylib"\]\|crate-type = \["rlib"\])$/crate-type = ["lib"]/' {head,base}/cedar-policy/Cargo.toml
	- run: rustup update ${{ matrix.toolchain }} && rustup default ${{ matrix.toolchain }}
	- run: cargo install cargo-semver-checks
	- run: cargo semver-checks check-release --package cedar-policy --baseline-root ../base
	working-directory: head

Provide feedback