build: add pnpm extension with specified version and integrity

Ensure that the same version of pnpm is used.

Author: alan-agius4

MODULE.bazel

@@ -60,6 +60,11 @@ node.toolchain(node_version_from_nvmrc = "//:.nvmrc")
 use_repo(node, "nodejs_toolchains")
 
 pnpm = use_extension("@aspect_rules_js//npm:extensions.bzl", "pnpm")
+pnpm.pnpm(
+    name = "pnpm",
+    pnpm_version = "10.26.0",
+    pnpm_version_integrity = "sha512-Oz9scl6+cSUGwKsa1BM8+GsfS2h+/85iqbOLTXLjlUJC5kMZD8UfoWQpScc19APevUT1yw7dZXq+Y6i2p+HkAg==",
+)
 use_repo(pnpm, "pnpm")
 
 npm = use_extension("@aspect_rules_js//npm:extensions.bzl", "npm")