ci: Install only the required nix tools

A previous commit allowed to select each tool separately on the toolbox.

This commit makes use of that for CI to possibly speed up loading from cachix
a little bit. It will also cause fewer cache misses when nix code is changed.

Resolves #3183

.github/workflows/test.yaml

@@ -44,7 +44,7 @@ jobs:
         uses: ./.github/actions/setup-nix
         with:
           authToken: '${{ secrets.CACHIX_AUTH_TOKEN }}'
-          tools: tests
+          tools: tests.coverage.bin tests.testDoctests.bin tests.testSpecIdempotence.bin
 
       - name: Run coverage (IO tests and Spec tests against PostgreSQL 15)
         run: postgrest-coverage
@@ -67,7 +67,7 @@ jobs:
     strategy:
       fail-fast: false
       matrix:
-        pgVersion: [9.6, 10, 11, 12, 13, 14, 15, 16]
+        pgVersion: ["9_6", 10, 11, 12, 13, 14, 15, 16]
     name: PG ${{ matrix.pgVersion }}
     runs-on: ubuntu-latest
     defaults:
@@ -81,7 +81,7 @@ jobs:
         uses: ./.github/actions/setup-nix
         with:
           authToken: '${{ secrets.CACHIX_AUTH_TOKEN }}'
-          tools: tests withTools
+          tools: tests.testSpec.bin tests.testIO.bin withTools.postgresql-${{ matrix.pgVersion }}.bin
 
       - name: Run spec tests
         if: always()
@@ -101,7 +101,7 @@ jobs:
         uses: ./.github/actions/setup-nix
         with:
           authToken: '${{ secrets.CACHIX_AUTH_TOKEN }}'
-          tools: memory
+          tools: memory.test.bin
       - name: Run memory tests
         run: postgrest-test-memory
 
@@ -117,7 +117,7 @@ jobs:
         uses: ./.github/actions/setup-nix
         with:
           authToken: '${{ secrets.CACHIX_AUTH_TOKEN }}'
-          tools: loadtest
+          tools: loadtest.loadtestAgainst.bin loadtest.report.bin
       - uses: WyriHaximus/github-action-get-previous-tag@04e8485ecb6487243907e330d522ff60f02283ce # v1.4.0
         id: get-latest-tag
         with: