Try caching the Docker image.

.github/workflows/tests.yml

@@ -23,7 +23,9 @@ jobs:
       if: matrix.os == 'macOS-latest'
 
     - name: Build Docker image
-      run: docker-compose -f Dockerfile.yml build sut
+      run: |
+        docker pull linuxbrew/brew
+        docker-compose -f Dockerfile.yml build sut
       if: matrix.os == 'ubuntu-latest'
 
     - name: Run brew test-bot

Dockerfile

@@ -26,6 +26,7 @@ RUN localedef -i en_US -f UTF-8 en_US.UTF-8 \
 	&& useradd -m -s /bin/bash linuxbrew \
 	&& echo 'linuxbrew ALL=(ALL) NOPASSWD:ALL' >>/etc/sudoers
 ADD . /home/linuxbrew/.linuxbrew/Homebrew
+ARG FORCE_REBUILD
 RUN cd /home/linuxbrew/.linuxbrew \
 	&& mkdir -p bin etc include lib opt sbin share var/homebrew/linked Cellar \
 	&& ln -s ../Homebrew/bin/brew /home/linuxbrew/.linuxbrew/bin/ \

Dockerfile.yml

@@ -1,5 +1,13 @@
+version: '3.7'
+
+services:
   sut:
-  build: .
+    build:
+      context: .
+      cache_from:
+        - linuxbrew/brew
+      args:
+        - FORCE_REBUILD=1
     command:
       - sh
       - -xc