Set timezone in CI

This seems like it was probably the cause of several time-of-day-specific test failures. Setting it (temporarily, I hope) in CI should probably mean we can keep testing WebKit (which isn’t otherwise affected by e.g. the `TZ` environment variable like the other browsers)

.github/workflows/ci.yml

@@ -19,6 +19,9 @@ defaults:
   run:
     shell: bash
 
+env:
+  TZ: 'America/Phoenix'
+
 jobs:
   changes:
     runs-on: 'ubuntu-latest'
@@ -95,9 +98,14 @@ jobs:
             packages/tree-sitter-xpath/types
           key: build-${{ matrix.node-version }}-${{ github.sha }}
 
-      - if: steps.cache-install.outputs.cache-hit != 'true'
-        run: 'yarn install --frozen-lockfile'
+      # `@odk/xpath` tests (currently) expect this time zone
+      - uses: szenius/[email protected]
+        with:
+          timezoneLinux: ${{ env.TZ }}
+          timezoneMacos: ${{ env.TZ }}
+          timezoneWindows: ${{ env.TZ }}
 
+      - run: 'yarn install --frozen-lockfile'
       - run: 'yarn build --force'
 
   lint:
@@ -226,6 +234,12 @@ jobs:
           key: build-${{ matrix.node-version }}-${{ github.sha }}
           fail-on-cache-miss: true
 
+      - uses: szenius/[email protected]
+        with:
+          timezoneLinux: ${{ env.TZ }}
+          timezoneMacos: ${{ env.TZ }}
+          timezoneWindows: ${{ env.TZ }}
+
       - run: 'yarn playwright install chromium firefox webkit && yarn playwright install-deps'
       # TODO: Browser/Node matrix
       - run: 'yarn workspace @odk/xpath test'