Remove --unsafe-perm from the FreeBSD build (#20565)

The `Build x86_64-unknown-freebsd (OXIDE)` job of the Release workflow
fails on `main` since #20550 ([latest
failure](https://github.com/tailwindlabs/tailwindcss/actions/runs/38272664961)):

```
npm error code EUNKNOWNCONFIG
npm error Unknown cli flag:
npm error   - --unsafe-perm
```

The FreeBSD package repository now installs `npm-12.0.2`, which rejects
unknown CLI flags. `--unsafe-perm` has been a no-op since npm 7, so this
PR removes it from `release.yml` and `prepare-release.yml`.

## Test plan

The Release workflow only runs on `main`, so the next push to `main`
verifies the fix.

.github/workflows/prepare-release.yml

@@ -174,7 +174,7 @@ jobs:
           shell: bash
           run: |
             sudo pkg install -y -f curl node libnghttp2 npm
-            sudo npm install -g pnpm@${{ env.PNPM_VERSION }} --unsafe-perm=true
+            sudo npm install -g pnpm@${{ env.PNPM_VERSION }}
             curl -sSf https://static.rust-lang.org/rustup/archive/1.27.1/x86_64-unknown-freebsd/rustup-init --output rustup-init
             chmod +x rustup-init
             ./rustup-init -y --profile minimal

.github/workflows/release.yml

@@ -178,7 +178,7 @@ jobs:
           shell: bash
           run: |
             sudo pkg install -y -f curl node libnghttp2 npm
-            sudo npm install -g pnpm@${{ env.PNPM_VERSION }} --unsafe-perm=true
+            sudo npm install -g pnpm@${{ env.PNPM_VERSION }}
             curl -sSf https://static.rust-lang.org/rustup/archive/1.27.1/x86_64-unknown-freebsd/rustup-init --output rustup-init
             chmod +x rustup-init
             ./rustup-init -y --profile minimal