Disable pnpm strict-dep-builds in stable-install-modes guard

pnpm 11.0.7+ turned `ignored build scripts` into a fatal
`ERR_PNPM_IGNORED_BUILDS`. Temp fixtures created by
`assert-stable-install-modes.mjs` install `@parcel/watcher` transitively
(via `@rspack/dev-server@^2`); its build script is unapproved in the
freshly-copied fixture, so `pnpm install` dies before the canary CLI
even runs. The 8 pnpm-mode failures in
https://github.com/extension-js/examples/actions/runs/25494125419/job/74809414463
are all this — bun/npm/yarn modes pass on the same canary.

Set `PNPM_CONFIG_STRICT_DEP_BUILDS=false` in the spawn env so pnpm 11
behaves like 10 (warn instead of fail). The guard exercises canary
install paths; it has no business gating on pnpm's policy-of-the-week
for build-script approval.

Author: cezaraugusto

scripts/assert-stable-install-modes.mjs

@@ -85,6 +85,14 @@ function run(command, args, cwd, env = {}) {
         COREPACK_ENABLE_AUTO_PIN: '0',
         PNPM_CONFIG_FROZEN_LOCKFILE: 'false',
         npm_config_frozen_lockfile: 'false',
+        // pnpm 11.0.7+ promoted "ignored build scripts" from a warning to a
+        // fatal `ERR_PNPM_IGNORED_BUILDS`. Temp fixtures created here pull in
+        // `@parcel/watcher` (transitive of `@rspack/dev-server@^2`) which has
+        // an unapproved build script, so a fresh pnpm install in the fixture
+        // dies before the canary even runs. Restore the pnpm 10 behaviour
+        // (warn-only) so this guard exercises canary install paths, not
+        // pnpm's policy-of-the-week.
+        PNPM_CONFIG_STRICT_DEP_BUILDS: 'false',
         ...env
       }
     })