ci: drop hardcoded CANN version from build cache key

Per review on #483: the cache key should not embed a CANN version
string. The container's CANN version is already governed solely by
the `image:` field of each job, so duplicating it in the key only
creates a second source of truth that can drift (e.g. an image bump
PR that forgets to update the key). When a forced cache invalidation
is genuinely needed, bump the v2 -> v3 prefix instead.

Removes the `cann8.5.0-` segment from all 5 cache keys (3 in
pr-test-npu.yml, 2 in push_build_cache.yml). Both sides update in
lockstep so push-side writes still match PR-side reads.

Co-Authored-By: Claude Opus 4.7 (1M context) <noreply@anthropic.com>

Author: JavaPythonAIForBAT

.github/workflows/pr-test-npu.yml

@@ -94,7 +94,7 @@ jobs:
         uses: runs-on/cache@v4
         with:
           path: output
-          key: sgl-kernel-npu-build-v2-${{ runner.os }}-a3-cann8.5.0-${{ steps.get_build_hash.outputs.BUILD_HASH }}
+          key: sgl-kernel-npu-build-v2-${{ runner.os }}-a3-${{ steps.get_build_hash.outputs.BUILD_HASH }}
 
       - name: Install dependencies
         run: |
@@ -465,7 +465,7 @@ jobs:
         uses: runs-on/cache@v4
         with:
           path: output
-          key: sgl-kernel-npu-build-v2-${{ runner.os }}-a3-cann8.5.0-${{ steps.get_build_hash.outputs.BUILD_HASH }}
+          key: sgl-kernel-npu-build-v2-${{ runner.os }}-a3-${{ steps.get_build_hash.outputs.BUILD_HASH }}
 
       - name: Install dependencies
         run: |
@@ -842,7 +842,7 @@ jobs:
         uses: runs-on/cache@v4
         with:
           path: output
-          key: sgl-kernel-npu-build-v2-${{ runner.os }}-a2-cann8.5.0-${{ steps.get_build_hash.outputs.BUILD_HASH }}
+          key: sgl-kernel-npu-build-v2-${{ runner.os }}-a2-${{ steps.get_build_hash.outputs.BUILD_HASH }}
 
       - name: Install dependencies
         run: |

.github/workflows/push_build_cache.yml

@@ -48,7 +48,7 @@ jobs:
         uses: runs-on/cache@v4
         with:
           path: output
-          key: sgl-kernel-npu-build-v2-${{ runner.os }}-a3-cann8.5.0-${{ steps.get_build_hash.outputs.BUILD_HASH }}
+          key: sgl-kernel-npu-build-v2-${{ runner.os }}-a3-${{ steps.get_build_hash.outputs.BUILD_HASH }}
 
       - name: Install dependencies
         if: steps.cache-build.outputs.cache-hit != 'true'
@@ -99,7 +99,7 @@ jobs:
         uses: runs-on/cache@v4
         with:
           path: output
-          key: sgl-kernel-npu-build-v2-${{ runner.os }}-a2-cann8.5.0-${{ steps.get_build_hash.outputs.BUILD_HASH }}
+          key: sgl-kernel-npu-build-v2-${{ runner.os }}-a2-${{ steps.get_build_hash.outputs.BUILD_HASH }}
 
       - name: Install dependencies
         if: steps.cache-build.outputs.cache-hit != 'true'