ci: use flake lock for tests

Ensure we don't have surprise breakages and can test against a specific
lock file.

Signed-off-by: Austin Horstman <khaneliman12@gmail.com>
(cherry picked from commit ac3c38be05ddb99b5863f5f4a57d24b542a62f30)

.github/workflows/test.yml

@@ -14,6 +14,7 @@ jobs:
     - uses: actions/checkout@v4
     - uses: cachix/install-nix-action@v31
       with:
+        # TODO: Adjust uninstall to not need channel
         nix_path: nixpkgs=channel:nixos-25.05
         extra_nix_config: |
           experimental-features = nix-command flakes
@@ -22,15 +23,15 @@ jobs:
           echo "Error: literalExample should be replaced by literalExpression" > /dev/stderr
           exit 1
         fi
-    - run: nix-build --show-trace -A docs.jsonModuleMaintainers
+    - run: nix build --show-trace .#docs-jsonModuleMaintainers
     - run: ./format --ci
-    - run: nix-shell --show-trace . -A install
-    - run: yes | home-manager -I home-manager=. uninstall
+    - run: nix run .#home-manager -- init --switch
+    - run: yes | nix run . -- uninstall
     - name: Run tests
-      run: nix-build -j auto --show-trace --arg enableBig false --pure --option allow-import-from-derivation false tests -A build.all
+      run: nix build -j auto --show-trace --option allow-import-from-derivation false --reference-lock-file flake.lock "./tests#test-all-no-big"
       env:
         GC_INITIAL_HEAP_SIZE: 4294967296
     - name: Run tests (with IFD)
-      run: nix-build -j auto --show-trace --arg enableBig false --pure --arg enableLegacyIfd true tests -A build.all
+      run: nix build -j auto --show-trace --reference-lock-file flake.lock "./tests#test-all-no-big"
       env:
         GC_INITIAL_HEAP_SIZE: 4294967296