dockerimg: set http.postBuffer for git inside container

We sometimes see failures with git push from the innie to the outie.
It appears to be when there is a big binary in the commit
(which is usually because of a different bug).
The internet suggests the HTTP POST limit in the git client
may be an issue (1MB in the git version in debian bookworm),
so let's bump it up.
diff --git a/dockerimg/testdata/testcreatedockerfile_empty_repo.dockerfile b/dockerimg/testdata/testcreatedockerfile_empty_repo.dockerfile
index cc73fbd..4b01973 100644
--- a/dockerimg/testdata/testcreatedockerfile_empty_repo.dockerfile
+++ b/dockerimg/testdata/testcreatedockerfile_empty_repo.dockerfile
@@ -4,18 +4,20 @@
 ARG GIT_USER_NAME
 
 RUN git config --global user.email "$GIT_USER_EMAIL" && \
-    git config --global user.name "$GIT_USER_NAME"
+    git config --global user.name "$GIT_USER_NAME" && \
+    git config --global http.postBuffer 524288000
 
-LABEL sketch_context="6f16c9b83fbd20e2eb242922989364954adb4905ab8c562baf2bc906ee347da5"
+LABEL sketch_context="7f08d4359542e0a924280791b6d7baae3480d3878b309e30eaf24d291b41e1df"
 COPY . /app
 
 WORKDIR /app
 RUN if [ -f go.mod ]; then go mod download; fi
 
-# Install any Python dependencies but continue if setup fails
-RUN if [ -f requirements.txt ]; then pip3 install -r requirements.txt || true; fi
+RUN set -eux; \
+    # Install any Python dependencies if applicable, continuing on failure
+    if [ -f requirements.txt ]; then pip3 install -r requirements.txt || true; fi
 
-# Ensure Go development tools are properly set up
-RUN go mod tidy || true
+# Ensure sketch binary is available
+RUN if [ ! -f /bin/sketch ]; then ln -s /app/sketch /bin/sketch || true; fi
 
 CMD ["/bin/sketch"]