test(NODE-5603): use npm 9 on eol node versions (#618)

Author: durran

.evergreen/config.yml

@@ -111,6 +111,8 @@ tasks:
         vars:
           NODE_LTS_VERSION: 16
       - func: install dependencies
+        vars:
+          NPM_VERSION: 9
       - func: run tests
         vars:
           TEST_TARGET: node
@@ -213,8 +215,11 @@ tasks:
     commands:
       - func: fetch source
         vars:
+          # This needs to stay pinned at Node v18.16.0 for consistency across perf runs.
           NODE_LTS_VERSION: v18.16.0
       - func: install dependencies
+        vars:
+          NPM_VERSION: 9
       - func: run benchmarks
         vars:
           WEB: false 

.evergreen/install-dependencies.sh

@@ -2,6 +2,9 @@
 set -o errexit  # Exit the script with error if any of the commands fail
 
 NODE_LTS_VERSION=${NODE_LTS_VERSION:-16}
+# npm version can be defined in the environment for cases where we need to install
+# a version lower than latest to support EOL Node versions.
+NPM_VERSION=${NPM_VERSION:-latest}
 
 source "${PROJECT_DIRECTORY}/.evergreen/init-node-and-npm-env.sh"
 
@@ -95,8 +98,7 @@ else
 fi
 
 if [[ $operating_system != "win" ]]; then
-  # Update npm to latest when we can
-  npm install --global npm@latest
+  npm install --global npm@$NPM_VERSION
   hash -r
 fi