Drop Windows CI .git/modules cache. (iree-org#12499)

As we're using shallow clones, this is providing dubious value. 1.7GB of
cache data is also cutting into our repo limit of 10GB, which may be
better used by ccache (recent runs are getting only 16% cache hits
reliably... need to also investigate that).

Test run:
https://github.com/openxla/iree/actions/runs/4326504405/jobs/7554009641

Progress on iree-org#11009

.github/workflows/ci.yml

@@ -202,17 +202,11 @@ jobs:
     steps:
       - name: "Checking out repository"
         uses: actions/checkout@ac593985615ec2ede58e132d2e21d2b1cbd6127c # v3.3.0
-      # Attempt to restore from caches unconditionally.
-      # Note: these will first try to grab a cache entry for this exact commit
-      #       then they will fall back to the latest for any commit.
+      # Attempt to restore from cache unconditionally.
+      # Note: this will first try to grab a cache entry for this exact commit
+      #       then it will fall back to the latest for any commit.
       # We're pretty limited on repository cache space (10GB) relative to cache
       # entry size (~2.5GB), so this usage is pretty optimistic.
-      - name: "Fetching cache (git submodules)"
-        uses: actions/cache/restore@58c146cc91c5b9e778e71775dfe9bf1442ad9a12 # v3.2.3
-        with:
-          path: .git/modules
-          key: gitmodules_all_windows_${{ github.sha }}
-          restore-keys: gitmodules_all_windows
       - name: "Fetching cache (CMake/ccache)"
         uses: actions/cache/restore@58c146cc91c5b9e778e71775dfe9bf1442ad9a12 # v3.2.3
         with:
@@ -250,13 +244,7 @@ jobs:
         run: ./build_tools/cmake/build_all.sh "${BUILD_DIR}"
       - name: "Testing IREE"
         run: ./build_tools/cmake/ctest_all.sh "${BUILD_DIR}"
-      # Write caches (if configured to) after all other steps are finished.
-      - name: "Saving cache (git submodules)"
-        if: needs.setup.outputs.write-caches == '1'
-        uses: actions/cache/save@58c146cc91c5b9e778e71775dfe9bf1442ad9a12 # v3.2.3
-        with:
-          path: .git/modules
-          key: gitmodules_all_windows_${{ github.sha }}
+      # Write cache (if configured to) after all other steps are finished.
       - name: "Saving cache (CMake/ccache)"
         if: needs.setup.outputs.write-caches == '1'
         uses: actions/cache/save@58c146cc91c5b9e778e71775dfe9bf1442ad9a12 # v3.2.3