chore(deps): update alpine docker tag to v3.22

| datasource | package | from | to   |
| ---------- | ------- | ---- | ---- |
| docker     | alpine  | 3.9  | 3.22 |


Signed-off-by: renovate-sh-app[bot] <219655108+renovate-sh-app[bot]@users.noreply.github.com>

Author: renovate-sh-app[bot]

app/Dockerfile

@@ -1,4 +1,4 @@
-FROM alpine:3.9
+FROM alpine:3.22@sha256:55ae5d250caebc548793f321534bc6a8ef1d116f334f18f4ada1b2daad3251b2
 ADD app /
 ADD index.html.tmpl /
 EXPOSE 80