plugins: Always install plugins with --no-save

The npm CLI can get confused if `package.json` or `package-lock.json`
exist.

.github/workflows/backend-tests.yml

@@ -58,7 +58,7 @@ jobs:
 
     - name: Install Etherpad plugins
       run: >
-        npm install
+        npm install --no-save
         ep_align
         ep_author_hover
         ep_cursortrace

.github/workflows/frontend-admin-tests.yml

@@ -28,7 +28,7 @@ jobs:
 
       # We intentionally install a much old ep_align version to test update minor versions
     - name: Install etherpad plugins
-      run: npm install ep_align@0.2.27
+      run: npm install --no-save ep_align@0.2.27
 
       # Nuke plugin tests
     - name: Install etherpad plugins

.github/workflows/frontend-tests.yml

@@ -65,7 +65,7 @@ jobs:
 
     - name: Install Etherpad plugins
       run: >
-        npm install
+        npm install --no-save
         ep_align
         ep_author_hover
         ep_cursortrace

.github/workflows/load-test.yml

@@ -52,7 +52,7 @@ jobs:
 
     - name: Install etherpad plugins
       run: >
-        npm install
+        npm install --no-save
         ep_align
         ep_author_hover
         ep_cursortrace