fix: allow TimeoutMinutes to be expression in Jobs (#1247)

This change stops act from rejecting valid entries such as

```
    timeout-minutes: ${{ matrix.runtime == 'v8' && 30 || 15 }}
```

at the job level.

This change complements the fix that was already in place
for the Step struct, done in #1217. See:

52f5c4592c

Co-authored-by: mergify[bot] <37929162+mergify[bot]@users.noreply.github.com>

pkg/model/workflow.go

@@ -63,7 +63,7 @@ type Job struct {
 	Env            yaml.Node                 `yaml:"env"`
 	If             yaml.Node                 `yaml:"if"`
 	Steps          []*Step                   `yaml:"steps"`
-	TimeoutMinutes int64                     `yaml:"timeout-minutes"`
+	TimeoutMinutes string                    `yaml:"timeout-minutes"`
 	Services       map[string]*ContainerSpec `yaml:"services"`
 	Strategy       *Strategy                 `yaml:"strategy"`
 	RawContainer   yaml.Node                 `yaml:"container"`