Fix some type errors.

pages/_app.tsx

@@ -24,7 +24,7 @@ import { ChatCircleText } from 'phosphor-react'
 TimeAgo.setDefaultLocale(en.locale)
 TimeAgo.addLocale(en)
 
-function MyApp({ Component, pageProps: { session, ...pageProps } }: AppProps) {
+function MyApp({ Component, pageProps: { session, ...pageProps } }: AppProps<{ session?: any }>) {
   const router = useRouter()
   const slug = router.query?.slug
   const gistId = (Array.isArray(slug) && slug[0]) ?? null

state/actions/fetchFiles.ts

@@ -1,5 +1,5 @@
 import { Octokit } from '@octokit/core'
-import state, { IFile } from '../index'
+import state, { IFile, ILang } from '../index'
 import { templateFileIds } from '../constants'
 
 const octokit = new Octokit()
@@ -48,7 +48,7 @@ export const fetchFiles = async (gistId: string) => {
 
     const files: IFile[] = Object.keys(res.data.files).map(filename => ({
       name: res.data.files?.[filename]?.filename || 'untitled.c',
-      language: res.data.files?.[filename]?.language?.toLowerCase() || '',
+      language: res.data.files?.[filename]?.language?.toLowerCase() as ILang | undefined,
       content: res.data.files?.[filename]?.content || ''
     }))