ci: bump the OBS deps cache key -- it was stuck on a permanently bad entry

actions/cache never overwrites an existing key: once a key has a saved
entry, later jobs' save steps are always skipped as a no-op regardless
of cache hit/miss. The very first job to ever populate this cache did
so before the "Drop non-relocatable OBS build tree" cleanup step
existed, so that entry included the bad, path-baked build_x86
directory -- and every run since has kept restoring that same bad
entry, not self-healing after "one more transitional run" the way it
looked when this was last checked. Confirmed live: a run just now hit
the identical stale-path CMakeCache.txt error against the same
original job hash (f72837d12c75c64a) from hours ago.

Bumping the key (obs-deps- -> obs-deps-v2-) is what actually forces a
fresh save under the cleanup step's watch, since the key content
(buildspec files) hasn't changed and nothing else would invalidate it.

Co-Authored-By: Claude Sonnet 5 <noreply@anthropic.com>
Claude-Session: https://claude.ai/code/session_01RL8abRmgFXkVASHkkqiJbE

.gitea/workflows/build.yml

@@ -80,7 +80,7 @@ jobs:
         uses: actions/cache@v4
         with:
           path: .deps
-          key: obs-deps-${{ runner.os }}-${{ hashFiles('cmake/macos/buildspec.cmake', 'cmake/common/buildspec_common.cmake', 'buildspec.json') }}
+          key: obs-deps-v2-${{ runner.os }}-${{ hashFiles('cmake/macos/buildspec.cmake', 'cmake/common/buildspec_common.cmake', 'buildspec.json') }}
 
       - name: Configure, build, test, verify
         run: .gitea/scripts/macos-build.sh
@@ -147,10 +147,22 @@ jobs:
         # needed: cmake/windows/buildspec.cmake's own download logic is
         # already idempotent, it just never gets the chance because .deps/
         # lives inside the checkout and is wiped by every fresh clone.
+        #
+        # The `v2` in the key: actions/cache never overwrites an existing
+        # key -- once a key has a saved entry, every later job's save step is
+        # skipped as a no-op, cache hit or not. The very first job ever
+        # to populate this cache did so BEFORE the "Drop non-relocatable OBS
+        # build tree" step below existed, so its save included the bad
+        # build_x86 directory -- and because saves under an existing key are
+        # permanently skipped, every run after that kept restoring that same
+        # bad entry forever, not "one more transitional run" as it looked at
+        # the time. Bumping the key is what actually forces a fresh save;
+        # bump it again (v3, ...) if this cache is ever found to be stale in
+        # a way a workflow change alone can't fix.
         uses: actions/cache@v4
         with:
           path: .deps
-          key: obs-deps-${{ runner.os }}-${{ hashFiles('cmake/windows/buildspec.cmake', 'cmake/common/buildspec_common.cmake', 'buildspec.json') }}
+          key: obs-deps-v2-${{ runner.os }}-${{ hashFiles('cmake/windows/buildspec.cmake', 'cmake/common/buildspec_common.cmake', 'buildspec.json') }}
 
       - name: Configure, build, test, verify
         # Windows PowerShell (powershell.exe), not PowerShell Core (pwsh) --