fix(ci): set RUNNER_TOOL_CACHE for setup-python action

The setup-python action defaults to /Users/runner which doesn't exist
on self-hosted runners. Set RUNNER_TOOL_CACHE to a writable temp path.

.gitea/workflows/ci.yml

@@ -4,6 +4,9 @@ name: CI
     branches: [master, crosspoint-ef]
   pull_request:
 
+env:
+  RUNNER_TOOL_CACHE: ${{ runner.temp }}/tool_cache
+
 jobs:
   build:
     runs-on: ubuntu-latest
@@ -12,6 +15,9 @@ jobs:
         with:
           submodules: recursive
 
+      - name: Set up Python tool cache directory
+        run: mkdir -p "$RUNNER_TOOL_CACHE"
+
       - uses: actions/setup-python@v5
         with:
           python-version: '3.12'

.gitea/workflows/release.yml

@@ -4,6 +4,9 @@ on:
     tags:
       - '*'
 
+env:
+  RUNNER_TOOL_CACHE: ${{ runner.temp }}/tool_cache
+
 jobs:
   build-release:
     runs-on: ubuntu-latest
@@ -19,6 +22,9 @@ jobs:
             ~/.platformio/.cache
           key: ${{ runner.os }}-pio
 
+      - name: Set up Python tool cache directory
+        run: mkdir -p "$RUNNER_TOOL_CACHE"
+
       - uses: actions/setup-python@v5
         with:
           python-version: '3.12'