Separate Postgres build dir from installation dir.

Previously, Postgres was built in 'tmp_install/build', and installed
into 'tmp_install'. In the CI, the 'build' directory was included in
the final neon.tar.zst artifact that includes all the necessary
binaries. That was unnecessary, the intermediate build results are not
needed, only the final binaries. Separate the build directory so that
the Postgres build happens in 'build', and it is installed into
'tmp_install'. That makes the final neon.tar.zst artifact smaller.

The changes to the python tests are needed to find the 'pg_regress'
binary in the installation directory. Previously, they would use the
'pg_regress' binary from the build directory, not the final
installation location.

.github/actions/run-python-test-set/action.yml

@@ -31,6 +31,13 @@ inputs:
 runs:
   using: "composite"
   steps:
+    - name: Checkout
+      if: inputs.needs_postgres_source == 'true'
+      uses: actions/checkout@v3
+      with:
+        submodules: true
+        fetch-depth: 1
+
     - name: Get Neon artifact for restoration
       uses: actions/download-artifact@v3
       with:
@@ -44,12 +51,11 @@ runs:
         tar -xf ./neon-artifact/neon.tar.zst -C /tmp/neon/
         rm -rf ./neon-artifact/
 
-    - name: Checkout
-      if: inputs.needs_postgres_source == 'true'
-      uses: actions/checkout@v3
-      with:
-        submodules: true
-        fetch-depth: 1
+        # Restore the parts of the 'build' directory that were included in the
+        # tarball. This includes the regression test modules in
+        # src/test/regress/*.so.
+        mkdir -p build/
+        cp -a /tmp/neon/pg_build/* build/
 
     - name: Cache poetry deps
       id: cache_poetry

.github/workflows/build_and_test.yml

@@ -88,7 +88,9 @@ jobs:
         id: cache_pg
         uses: actions/cache@v3
         with:
-          path: tmp_install/
+          path: |
+            tmp_install/
+            build/src/test/regress/*.so
           key: v1-${{ runner.os }}-${{ matrix.build_type }}-pg-${{ steps.pg_ver.outputs.pg_rev }}-${{ hashFiles('Makefile') }}
 
       - name: Build postgres
@@ -143,7 +145,12 @@ jobs:
           fi
 
       - name: Install postgres binaries
-        run: cp -a tmp_install /tmp/neon/pg_install
+        run: |
+          cp -a tmp_install /tmp/neon/pg_install
+
+          # Include modules needed by the Postgres regression tests
+          mkdir -p /tmp/neon/pg_build/src/test/regress
+          cp -a build/src/test/regress/*.so /tmp/neon/pg_build/src/test/regress
 
       - name: Prepare neon artifact
         run: ZSTD_NBTHREADS=0 tar -C /tmp/neon/ -cf ./neon.tar.zst --zstd .