fix(actions): evaluate each ${{ }} part on its own (#38754) (#38797)

Backport of https://github.com/go-gitea/gitea/pull/38754

Every `${{ }}` part was spliced as raw text into a synthesized
`format('...', <raw>)` call and re-parsed, so unbalanced parentheses
restructured the whole expression:

```yaml
run-name: ${{ 1) && (2 }}          # panicked, aborting workflow parsing for the push
if: ${{ 1 }} ${{ 0) && (0 }}       # silently skipped the job
runs-on: ${{ nosuchcontext.x }}    # silently queued the job against the label ""
```

One scanner shaped like GitHub's template reader now splits every value
and each part is evaluated on its own, so nothing builds an expression
out of text. A part that fails is an error instead of an empty string.

`expressionCallsFunction` is self-contained here, since this branch has
no `expressionsMatch` to build it on. That makes
`github.com/rhysd/actionlint` a direct dependency, which it already is
on `main`.

go.mod

@@ -87,6 +87,7 @@ require (
 	github.com/prometheus/client_golang v1.23.2
 	github.com/quasoft/websspi v1.1.2
 	github.com/redis/go-redis/v9 v9.21.0
+	github.com/rhysd/actionlint v1.7.12
 	github.com/robfig/cron/v3 v3.0.1
 	github.com/santhosh-tekuri/jsonschema/v6 v6.0.2
 	github.com/sassoftware/go-rpmutils v0.4.0
@@ -244,7 +245,6 @@ require (
 	github.com/prometheus/common v0.68.1 // indirect
 	github.com/prometheus/procfs v0.20.1 // indirect
 	github.com/remyoudompheng/bigfft v0.0.0-20230129092748-24d4a6f8daec // indirect
-	github.com/rhysd/actionlint v1.7.12 // indirect
 	github.com/rs/xid v1.6.0 // indirect
 	github.com/russross/blackfriday/v2 v2.1.0 // indirect
 	github.com/shopspring/decimal v1.4.0 // indirect