Don't cache Elixir build in static_analysis workflow (#1227)

Still [having
issues](https://github.com/firezone/firezone/actions/runs/3759257641)
with the Elixir cache.

Things tried that didn't work:
- Namespacing by branch name. Github does this already.
- Removing the `restore-keys` in order to only restore the cache if it's
a direct hit.

The `static_analysis` workflow runs `mix compile --force
--warnings-as-errors` which doesn't use the build cache, so it's
removed, which fixes the problem.

.github/workflows/static_analysis.yml

@@ -29,15 +29,17 @@ jobs:
         with:
           otp-version: '25'
           elixir-version: '1.14'
-      - uses: actions/cache@v3.0.11
-        name: Setup Elixir cache
+      - uses: actions/cache@v3
+        name: Elixir Deps Cache
+        env:
+          cache-name: cache-elixir-deps
         with:
-          path: |
-            deps
-            _build
-          key: ${{ runner.os }}-${{ github.ref }}-mix-otp-25-${{ hashFiles('**/mix.lock') }}
+          # XXX: We've purposefully omitted caching the _build directory here because we
+          # force-recompile in the pre-commit run below in order to catch any compilation warnings.
+          path: deps
+          key: ${{ github.workflow }}-${{ runner.os }}-${{ env.cache-name }}-${{ hashFiles('**/mix.lock') }}
           restore-keys: |
-            ${{ runner.os }}-${{ github.ref }}-mix-otp-25-${{ hashFiles('**/mix.lock') }}
+            ${{ github.workflow }}-${{ runner.os }}-${{ env.cache-name }}-
       - uses: actions/cache@v3.0.11
         name: Setup ruby cache
         with:

.github/workflows/test.yml

@@ -36,14 +36,22 @@ jobs:
         with:
           otp-version: '25'
           elixir-version: '1.14'
-      - uses: actions/cache@v3.0.11
+      - uses: actions/cache@v3
+        name: Elixir Deps Cache
+        env:
+          cache-name: cache-elixir-deps
         with:
-          path: |
-            deps
-            _build
-          key: ${{ runner.os }}-${{ github.ref }}-mix-otp-25-${{ hashFiles('**/mix.lock') }}
+          path: deps
+          key: ${{ runner.os }}-${{ env.cache-name }}-${{ hashFiles('**/mix.lock') }}
           restore-keys: |
-            ${{ runner.os }}-${{ github.ref }}-mix-otp-25-${{ hashFiles('**/mix.lock') }}
+            ${{ runner.os }}-${{ env.cache-name }}-
+      - uses: actions/cache@v3
+        name: Elixir Build Cache
+        env:
+          cache-name: cache-elixir-build
+        with:
+          path: _build
+          key: ${{ runner.os }}-${{ env.cache-name }}-${{ hashFiles('**/mix.lock') }}
       - name: Install Dependencies
         run: mix deps.get --only $MIX_ENV
       - name: Setup Database