Fix error handling when building image

Apparently, we managed to publish an image without working aiohttp
because of this.

Partially a regression from 5d7183a.

Dockerfile

@@ -17,7 +17,8 @@ COPY babel.cfg /opt/snikket-web-portal/babel.cfg
 
 WORKDIR /opt/snikket-web-portal
 
-RUN pip3 install -r requirements.txt; \
+RUN set -eu; \
+    pip3 install -r requirements.txt; \
     pip3 install -r build-requirements.txt; \
     make;
 
@@ -47,7 +48,7 @@ RUN set -eu; \
 WORKDIR /opt/snikket-web-portal
 
 COPY requirements.txt /opt/snikket-web-portal/requirements.txt
-RUN pip3 install -r requirements.txt; rm -rf /root/.cache;
+RUN set -eu; pip3 install -r requirements.txt; rm -rf /root/.cache;
 
 COPY --from=build /opt/snikket-web-portal/snikket_web/ /opt/snikket-web-portal/snikket_web
 COPY babel.cfg /opt/snikket-web-portal/babel.cfg

snikket_web/infra.py

@@ -8,7 +8,6 @@ import quart.flask_patch  # noqa:F401
 from quart import (
     current_app,
     request,
-    g,
 )
 
 import flask_babel
@@ -35,9 +34,6 @@ BYTE_UNIT_SCALE_MAP = [
 
 @babel.localeselector  # type:ignore
 def selected_locale() -> str:
-    # Needs mypy ignore because this is a free-for-all object and has no
-    # publicly known attributes.
-    g.language_header_accessed = True  # type: ignore
     selected = request.accept_languages.best_match(
         current_app.config['LANGUAGES']
     ) or current_app.config['LANGUAGES'][0]
@@ -72,12 +68,6 @@ def format_bytes(n: float) -> str:
     return "{} {}".format(n, unit)
 
 
-def add_vary_language_header(resp: quart.Response) -> quart.Response:
-    if getattr(g, "language_header_accessed", False):
-        resp.vary.add("Accept-Language")
-    return resp
-
-
 def init_templating(app: quart.Quart) -> None:
     app.template_filter("repr")(repr)
     app.template_filter("format_datetime")(flask_babel.format_datetime)
@@ -88,7 +78,6 @@ def init_templating(app: quart.Quart) -> None:
     app.template_filter("format_bytes")(format_bytes)
     app.template_filter("flatten")(flatten)
     app.template_filter("circle_name")(circle_name)
-    app.after_request(add_vary_language_header)
 
 
 def generate_error_id() -> str: