build(deps): bump alpine from 3.18.5 to 3.19.1 in /build-container

Bumps alpine from 3.18.5 to 3.19.1.

---
updated-dependencies:
- dependency-name: alpine
  dependency-type: direct:production
  update-type: version-update:semver-minor
...

Signed-off-by: dependabot[bot] <[email protected]>

build-container/Dockerfile

@@ -1,4 +1,4 @@
-FROM alpine:3.18.5
+FROM alpine:3.19.1
 RUN apk add --no-cache python3 python3-dev musl-dev libxml2 libxml2-dev libxslt libxslt-dev gcc
 RUN python3 -m ensurepip
 RUN pip3 install docx-mailmerge==0.5.0