fix: downgrade ERR_PNPM_IGNORED_BUILDS to a warning (#7527)

Plugin CI is still failing on ERR_PNPM_IGNORED_BUILDS even with the
build-script policy declared in both pnpm-workspace.yaml (#7523) and
package.json (#7525). pnpm's strict-dep-builds defaults to true in 10+,
so any transitive dep with an unrecognized postinstall fails the build.

For etherpad-lite — and especially for downstream plugin repos that
pull this codebase as their core install — that's a footgun: the moment
some new transitive ships a postinstall, every plugin's CI explodes.

Set strictDepBuilds: false in pnpm-workspace.yaml AND
strict-dep-builds=false in .npmrc as a defensive layer, so unknown
postinstalls become a warning instead of a hard failure. The
allow/ignore lists still control what actually runs.

Co-authored-by: Claude Opus 4.6 (1M context) <noreply@anthropic.com>

.npmrc

@@ -0,0 +1 @@
+strict-dep-builds=false

pnpm-workspace.yaml

@@ -11,3 +11,7 @@ onlyBuiltDependencies:
 # encountered as transitive deps (e.g. scarf pulled in via swagger-ui-dist).
 ignoredBuiltDependencies:
   - '@scarf/scarf'
+# Belt-and-suspenders: even if a fresh transitive dep slips through with a
+# postinstall script, downgrade to a warning so CI doesn't break for
+# downstream plugin repos that pull etherpad-lite as their core install.
+strictDepBuilds: false