fix(ci): actions/cache@v4 加 continue-on-error——缓存故障不阻断 job

所有 5 个 actions/cache@v4 步骤加 continue-on-error: true：
- validate-style pip cache
- validate-security pip cache
- validate-python pip cache
- unit-tests pip cache
- frontend-unit-test npm cache

当 Gitea Actions 缓存基础设施出现瞬态故障（git cache EOF /
归档损坏）时，cache restore 步骤会标黄但不中断 job，
后续的 pip install 重试逻辑自动 fresh download 兜底。

.gitea/workflows/ci-pipeline.yml

@@ -150,6 +150,7 @@ jobs:
       run: bash scripts/ci/step_timer_start.sh
     - name: Cache pip dependencies
       uses: actions/cache@v4
+      continue-on-error: true
       with:
         path: /root/.cache/pip
         key: ${{ runner.os }}-pip-style-${{ hashFiles('requirements*.txt') }}
@@ -252,6 +253,7 @@ jobs:
       run: bash scripts/ci/step_timer_start.sh
     - name: Cache pip dependencies
       uses: actions/cache@v4
+      continue-on-error: true
       with:
         path: /root/.cache/pip
         key: ${{ runner.os }}-pip-security-${{ hashFiles('requirements*.txt') }}
@@ -352,6 +354,7 @@ jobs:
       run: bash scripts/ci/step_timer_start.sh
     - name: Cache pip dependencies
       uses: actions/cache@v4
+      continue-on-error: true
       with:
         path: /root/.cache/pip
         key: ${{ runner.os }}-pip-python-${{ hashFiles('requirements*.txt') }}
@@ -456,6 +459,7 @@ jobs:
       run: bash scripts/ci/step_install_ffmpeg.sh
     - name: Cache pip dependencies
       uses: actions/cache@v4
+      continue-on-error: true
       with:
         path: /root/.cache/pip
         key: ${{ runner.os }}-pip-unittests-${{ hashFiles('requirements*.txt') }}
@@ -664,6 +668,7 @@ jobs:
       run: bash scripts/ci/step_timer_start.sh
     - name: Cache npm dependencies
       uses: actions/cache@v4
+      continue-on-error: true
       with:
         path: /root/.npm
         key: ${{ runner.os }}-npm-vitest-${{ hashFiles('apps/web/package-lock.json') }}