btrfs-progs: ci: fix lcov warnings on unexecuted blocks

There's a report on the CI after base ubuntu image update:

geninfo: WARNING:
/home/runner/work/btrfs-progs/btrfs-progs/common/device-scan.c:429:
unexecuted block on non-branch line with non-zero hit count.  Use
"geninfo --rc geninfo_unexecuted_blocks=1 to set count to zero.
	(use "geninfo --ignore-errors gcov,gcov ..." to suppress this warning)

Signed-off-by: David Sterba <dsterba@suse.com>

.github/workflows/coverage.yml

@@ -44,7 +44,7 @@ jobs:
       - name: Generate lcov results
         run: |
           lcov -c -d . -o lcov-info
-          genhtml -o lcov-out lcov-info
+          genhtml --rc geninfo_unexecuted_blocks=1 -o lcov-out lcov-info
       - name: Save lcov results
         uses: actions/upload-artifact@v4
         with: