node: Fix generator ripgrep binary mappings and add missing architectures

The @vscode/ripgrep package postinstall script expects specific binary
variants for each architecture. This patch:

1. Fixes aarch64 to use musl variant instead of gnu
   - Both variants exist, but postinstall expects musl
   - Aligns with x86_64 and i386 (which also use musl)

2. Adds missing architecture mappings for ppc64, riscv64, and s390x
   - These architectures are supported by @vscode/ripgrep
   - Uses gnu variants (only available option for these arches)

This causes the postinstall script to fail to find the cached binary
and attempt to download from GitHub, which fails in offline build
environments (RPM builds, air-gapped systems, etc).

The mappings now match exactly what the postinstall script expects:
https://github.com/microsoft/vscode-ripgrep/blob/main/lib/postinstall.js#L38-L47

Assisted-by: Claude Code

Author: LorbusChris

node/flatpak_node_generator/providers/special.py

@@ -307,7 +307,10 @@ async def get_ripgrep_tag(version: str) -> str:
             'x86_64': 'x86_64-unknown-linux-musl',
             'i386': 'i686-unknown-linux-musl',
             'arm': 'arm-unknown-linux-gnueabihf',
-            'aarch64': 'aarch64-unknown-linux-gnu',
+            'aarch64': 'aarch64-unknown-linux-musl',
+            'ppc64': 'powerpc64le-unknown-linux-gnu',
+            'riscv64': 'riscv64gc-unknown-linux-gnu',
+            's390x': 's390x-unknown-linux-gnu',
         }
         destdir = self.gen.data_root / 'tmp' / f'vscode-ripgrep-cache-{package.version}'
         for arch, ripgrep_arch in ripgrep_arch_map.items():