Specify pnpm version

Author: Demivan

.github/workflows/ shipjs-trigger.yml

@@ -19,6 +19,7 @@ jobs:
           node-version: '14'
       - uses: pnpm/action-setup@v2.0.1
         with:
+          version: 6.x.x
           run_install: true
       - run: npx shipjs trigger
         env:

.github/workflows/test.yml

@@ -26,6 +26,7 @@ jobs:
           node-version: ${{ matrix.node }}
       - uses: pnpm/action-setup@v2.0.1
         with:
+          version: 6.x.x
           run_install: true
 
       - name: Test
@@ -44,6 +45,7 @@ jobs:
       - uses: actions/setup-node@v2.4.1
       - uses: pnpm/action-setup@v2.0.1
         with:
+          version: 6.x.x
           run_install: true
 
       - name: Lint