Downsize builders for i686-gnu

The infra-team is continuously monitoring the efficiency of the build
system in an effort to improve overall build times and resource usage.
The builders for the `i686-gnu` targets have used much less resources
than allocated in the past, so we are testing a smaller builder size for
them.

.github/workflows/ci.yml

@@ -260,10 +260,10 @@ jobs:
             os: ubuntu-20.04-8core-32gb
             env: {}
           - name: i686-gnu
-            os: ubuntu-20.04-16core-64gb
+            os: ubuntu-20.04-8core-32gb
             env: {}
           - name: i686-gnu-nopt
-            os: ubuntu-20.04-16core-64gb
+            os: ubuntu-20.04-8core-32gb
             env: {}
           - name: mingw-check
             os: ubuntu-20.04-8core-32gb

src/ci/github-actions/ci.yml

@@ -416,10 +416,10 @@ jobs:
             <<: *job-linux-8c
 
           - name: i686-gnu
-            <<: *job-linux-16c
+            <<: *job-linux-8c
 
           - name: i686-gnu-nopt
-            <<: *job-linux-16c
+            <<: *job-linux-8c
 
           - name: mingw-check
             <<: *job-linux-8c