tests: Pass --legacy-peer-deps flag to work around npm v7 bug

This flag is unknown to npm v6, but npm v6 silently ignores unknown
flags.

.github/workflows/backend-tests.yml

@@ -57,8 +57,10 @@ jobs:
         sudo apt install -y --no-install-recommends libreoffice libreoffice-pdfimport
 
     - name: Install Etherpad plugins
+      # The --legacy-peer-deps flag is required to work around a bug in npm v7:
+      # https://github.com/npm/cli/issues/2199
       run: >
-        npm install --no-save
+        npm install --no-save --legacy-peer-deps
         ep_align
         ep_author_hover
         ep_cursortrace
@@ -134,8 +136,10 @@ jobs:
         node-version: 12
 
     - name: Install Etherpad plugins
+      # The --legacy-peer-deps flag is required to work around a bug in npm v7:
+      # https://github.com/npm/cli/issues/2199
       run: >
-        npm install --no-save
+        npm install --no-save --legacy-peer-deps
         ep_align
         ep_author_hover
         ep_cursortrace

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

@@ -23,7 +23,9 @@ jobs:
 
     - name: Install etherpad plugins
       # We intentionally install an old ep_align version to test upgrades to the minor version number.
-      run: npm install --no-save ep_align@0.2.27
+      # The --legacy-peer-deps flag is required to work around a bug in npm v7:
+      # https://github.com/npm/cli/issues/2199
+      run: npm install --no-save --legacy-peer-deps ep_align@0.2.27
 
     # This must be run after installing the plugins, otherwise npm will try to
     # hoist common dependencies by removing them from src/node_modules and

.github/workflows/frontend-tests.yml

@@ -62,8 +62,10 @@ jobs:
       run: src/tests/frontend/travis/sauce_tunnel.sh
 
     - name: Install Etherpad plugins
+      # The --legacy-peer-deps flag is required to work around a bug in npm v7:
+      # https://github.com/npm/cli/issues/2199
       run: >
-        npm install --no-save
+        npm install --no-save --legacy-peer-deps
         ep_align
         ep_author_hover
         ep_cursortrace

.github/workflows/load-test.yml

@@ -51,8 +51,10 @@ jobs:
       run: sudo npm install -g etherpad-load-test
 
     - name: Install etherpad plugins
+      # The --legacy-peer-deps flag is required to work around a bug in npm v7:
+      # https://github.com/npm/cli/issues/2199
       run: >
-        npm install --no-save
+        npm install --no-save --legacy-peer-deps
         ep_align
         ep_author_hover
         ep_cursortrace