Upgrade deno to v1.24.0 to be compatible with esm.sh's handlebars

Earlier versions of deno report the following error when running the
tests

```
Check file:///home/runner/work/handlebars/handlebars/tests/basic.test.ts
error: TS2322 [ERROR]: Type 'AliasName<K, A>' is not assignable to type
'string | number | symbol'.
  Type 'K | (string extends A[K] ? K : A[K] extends string ? K | A[K] :
  K)' is not assignable to type 'string | number | symbol'.
      Type 'string extends A[K] ? K : A[K] extends string ? K | A[K] :
      K' is not assignable to type 'string | number | symbol'.
      ...
```

Author: mocoso

.github/workflows/ci.yml

@@ -7,7 +7,7 @@ jobs:
         runs-on: ubuntu-18.04
         strategy:
             matrix:
-                deno: [1.18.1]
+                deno: [1.24.0]
         name: Deno ${{ matrix.deno }}
         steps:
             - uses: actions/checkout@master