build.yml: route 4 fourier-debian jobs to debian-aarch64 (bohr)

Native trixie execution avoids the cross-distro ABI skew issues we
hit when building libva-v4l2-request-fourier-debian on Arch (PR #44):
__vaDriverInit_1_23 vs trixies libva 2.22 binding. The same hazard
applies to other fourier-debian jobs that link against debian libs.

Jobs moved from runs-on: arch-aarch64 -> debian-aarch64:
- ffmpeg-v4l2-request-debian
- mpv-fourier-debian
- daedalus-v4l2-debian
- daedalus-v4l2-dkms-debian

Left alone (arch=all, no native compile against debian libs):
- lmcp-debian
- claude-his-debian

Depends on PR #46 (runs-on uses bohrs LABEL, not runner-name).

.gitea/workflows/build.yml

@@ -906,7 +906,7 @@ jobs:
   # -------------------------------------------------------------------------
   ffmpeg-v4l2-request-debian:
     needs: ffmpeg-v4l2-request-aarch64
-    runs-on: arch-aarch64
+    runs-on: debian-aarch64
     continue-on-error: true
     steps:
       - uses: actions/checkout@v4
@@ -1045,7 +1045,7 @@ jobs:
   # -------------------------------------------------------------------------
   mpv-fourier-debian:
     needs: mpv-fourier-aarch64
-    runs-on: arch-aarch64
+    runs-on: debian-aarch64
     continue-on-error: true
     steps:
       - uses: actions/checkout@v4
@@ -1131,7 +1131,7 @@ jobs:
   # -------------------------------------------------------------------------
   daedalus-v4l2-debian:
     needs: claude-his-debian
-    runs-on: arch-aarch64
+    runs-on: debian-aarch64
     continue-on-error: true
     steps:
       - uses: actions/checkout@v4
@@ -1220,7 +1220,7 @@ jobs:
   # -------------------------------------------------------------------------
   daedalus-v4l2-dkms-debian:
     needs: daedalus-v4l2-debian
-    runs-on: arch-aarch64
+    runs-on: debian-aarch64
     continue-on-error: true
     steps:
       - uses: actions/checkout@v4