Another attempt at fixing the docker bake error (#33535)

Turns out the .env.docker:build is read automatically by nx when running
that project step, so it should be in the env. It might just be that using
the `x=$x` format means docker gets the $ literally because no shell is involved
here, so we need to use the plain `x` format so docker knows to take it from
the environment itself.

That's the theory, anyway.

packages/playwright-common/project.json

@@ -32,8 +32,7 @@
                 "platforms": ["linux/amd64", "linux/arm64"],
                 "provenance": "true",
                 "sbom": true,
-                "env-file": ["{projectRoot}/.env.docker:build"],
-                "build-args": ["PLAYWRIGHT_VERSION=$PLAYWRIGHT_VERSION"],
+                "build-args": ["PLAYWRIGHT_VERSION"],
                 "context": "{projectRoot}",
                 "metadata": {
                     "images": ["ghcr.io/element-hq/element-web/playwright-server"],