Stop relying on the master version of Psalm

I just got bitten by a bug on master at
https://github.com/doctrine/sql-formatter/pull/43#issuecomment-615576443,
and there are good chances we have the bug on the Dbal too. Anyway, it
only makes sense to use the same version as in the vendors.

.github/workflows/continuous-integration.yml

@@ -8,9 +8,26 @@ jobs:
   static-analysis-psalm:
     name: Static Analysis with Psalm
     runs-on: ubuntu-latest
+
     steps:
       - name: Checkout code
         uses: actions/checkout@v2
 
+      - name: "Install PHP"
+        uses: "shivammathur/setup-php@1.8.1"
+        with:
+          coverage: "none"
+          php-version: "7.4"
+
+      - name: "Cache dependencies installed with composer"
+        uses: "actions/cache@v1.0.3"
+        with:
+          path: "~/.composer/cache"
+          key: "composer-${{ hashFiles('composer.json') }}"
+          restore-keys: "composer-"
+
+      - name: "Install dependencies with composer"
+        run: "composer update --no-interaction --no-progress --no-suggest"
+
       - name: Psalm
-        uses: docker://vimeo/psalm-github-actions
+        run: "vendor/bin/psalm"