Fix assigning RTIME literal to RTIME variable

[MasonM]

Currently, trying to assign an RTIME literal to an RTIME variable (e.g. beresp.ttl) triggers the error "RTIME literal could not assign to RTIME". However, the linter allows this:

falco/linter/operator.go

Lines 56 to 60 in 87715d6

	case types.RTimeType, types.TimeType:
	switch right {
	// allows both variable and literal
	case types.RTimeType, types.TimeType:
	return

I double-checked using Fiddle: https://fiddle.fastly.dev/fiddle/fe4fb73d

[richardmarshall]

TIME variables should also be able to have a RTIME literal assigned, could you fix that too?

falco/interpreter/assign/assign.go

Lines 197 to 199 in 87715d6

	if right.IsLiteral() {
	return errors.WithStack(fmt.Errorf("RTIME literal could not assign to TIME"))
	}

Validity of that assignment shown here: https://fiddle.fastly.dev/fiddle/f663accf

[MasonM]

@richardmarshall You're right! Done in 9a9ec61

[richardmarshall]

LGTM

[ysugimoto]

Thanks both, looks very good!