ci: pass NIX_CONFIG with GitHub token into all test containers

- Add NIX_CONFIG with GitHub access token to all CI test workflows
- Export NIX_CONFIG in Makefile for propagation to test scripts
- Forward NIX_CONFIG explicitly into all docker run invocations
- Prevent GitHub API rate limit errors during Nix-based tests

https://chatgpt.com/share/69432655-a948-800f-8c0d-353921cdf644

scripts/test/test-e2e.sh

@@ -11,6 +11,7 @@ docker run --rm \
   -v "pkgmgr_nix_cache_${PKGMGR_DISTRO}:/root/.cache/nix" \
   -e REINSTALL_PKGMGR=1 \
   -e TEST_PATTERN="${TEST_PATTERN}" \
+  -e NIX_CONFIG="${NIX_CONFIG}" \
   --workdir /opt/src/pkgmgr \
   "pkgmgr-${PKGMGR_DISTRO}" \
   bash -lc '

scripts/test/test-env-nix.sh

@@ -14,6 +14,7 @@ docker run --rm \
   -v "pkgmgr_nix_cache_${PKGMGR_DISTRO}:/root/.cache/nix" \
   --workdir /opt/src/pkgmgr \
   -e REINSTALL_PKGMGR=1 \
+  -e NIX_CONFIG="${NIX_CONFIG}" \
   "${IMAGE}" \
   bash -lc '
     set -euo pipefail

scripts/test/test-env-virtual.sh

@@ -19,6 +19,7 @@ if OUTPUT=$(docker run --rm \
     -e REINSTALL_PKGMGR=1 \
     -v "$(pwd):/opt/src/pkgmgr" \
     -w /opt/src/pkgmgr \
+    -e NIX_CONFIG="${NIX_CONFIG}" \
     "${IMAGE}" \
     bash -lc '
         set -euo pipefail

scripts/test/test-integration.sh

@@ -12,6 +12,7 @@ docker run --rm \
   --workdir /opt/src/pkgmgr \
   -e REINSTALL_PKGMGR=1 \
   -e TEST_PATTERN="${TEST_PATTERN}" \
+  -e NIX_CONFIG="${NIX_CONFIG}" \
   "pkgmgr-${PKGMGR_DISTRO}" \
   bash -lc '
     set -e;

scripts/test/test-unit.sh

@@ -12,6 +12,7 @@ docker run --rm \
   --workdir /opt/src/pkgmgr \
   -e REINSTALL_PKGMGR=1 \
   -e TEST_PATTERN="${TEST_PATTERN}" \
+  -e NIX_CONFIG="${NIX_CONFIG}" \
   "pkgmgr-${PKGMGR_DISTRO}" \
   bash -lc '
     set -e;