Revert upstream's upload-artifact v7->v8 bump

Upstream Fuse 0b4c6dd ("Align upload-artifact to v8 across all
workflows") bumped the four upload-artifact references from v7 to v8 to
match the download-artifact pins. v8 exists for download-artifact (latest
v8.0.1) but not for upload-artifact (max v7.0.1); the bump silently broke
upstream's CI and arrives here via this merge. Revert those four lines so
the workflows resolve their action versions on github.com.

Author: morozov

.github/workflows/build_libspectrum_linux_sub.yml

@@ -139,7 +139,7 @@ jobs:
           -C /usr/local/ -T.tar_files
 
       - name: (12) Upload generated tar file
-        uses: actions/upload-artifact@v8
+        uses: actions/upload-artifact@v7
         with:
           name: libspectrum-installed-linux-${{ inputs.key }}
           path: |

.github/workflows/build_libspectrum_macos_sub.yml

@@ -144,7 +144,7 @@ jobs:
           -C /usr/local/ -T.tar_files
 
       - name: (12) Upload generated tar file
-        uses: actions/upload-artifact@v8
+        uses: actions/upload-artifact@v7
         with:
           name: libspectrum-installed-macos-${{ inputs.key }}
           path: |

.github/workflows/build_libspectrum_windows_sub.yml

@@ -223,7 +223,7 @@ jobs:
           -C /usr/local/i686-w64-mingw32/ .
 
       - name: (15) Upload generated tar file
-        uses: actions/upload-artifact@v8
+        uses: actions/upload-artifact@v7
         with:
           name: libspectrum-installed-windows-${{ inputs.key }}
           path: |

.github/workflows/build_windows_sub.yml

@@ -495,7 +495,7 @@ jobs:
 
       - name: (11) Upload generated artifact(s)
         if: ${{ inputs.upload_artifacts }}
-        uses: actions/upload-artifact@v8
+        uses: actions/upload-artifact@v7
         with: 
           name: ${{ steps.rename-files.outputs.FUSE_DISTR_BASE }}
           if-no-files-found: error