tools/bazel: remove .bazelrc.sandbox from checksum

This avoids recreating the sandbox on the second run on a clean
checkout. The file is autogenerated by tools/bazel, if the user
chooses to modify it manually, that's on them.

Should fix half of https://github.com/monogon-dev/monogon/issues/172.

Change-Id: Id43d4c351f69c78ff7a4cd25b5bef84a632ff2b2
Reviewed-on: https://review.monogon.dev/c/monogon/+/1116
Reviewed-by: Lorenz Brun <lorenz@monogon.tech>
Tested-by: Jenkins CI
diff --git a/tools/bazel b/tools/bazel
index 2063a3f..849bb9b 100755
--- a/tools/bazel
+++ b/tools/bazel
@@ -101,7 +101,6 @@
   local checksum_file="${SANDBOX}/checksum"
   local checksum_input=(
     ${DIR}/../third_party/sandboxroot/{repositories.bzl,BUILD.bazel}
-    ${DIR}/../.bazelrc.sandbox
     ${DIR}/../.bazelrc.sandboxroot
     ${DIR}/../tools/bazel
   )
@@ -130,6 +129,9 @@
   cp /etc/resolv.conf "${ROOT}/.bazeldnf/sandbox/default/root/etc/resolv.conf"
 
   cat > "${DIR}/../.bazelrc.sandbox" <<EOF
+# Autogenerated by tools/bazel. Manual changes can result in stale caches.
+# Modify the generator instead.
+
 build --sandbox_add_mount_pair=${ROOT}/.bazeldnf/sandbox/default/root/etc:/etc
 build --sandbox_add_mount_pair=${ROOT}/.bazeldnf/sandbox/default/root/usr:/usr
 build --sandbox_add_mount_pair=${ROOT}/.bazeldnf/sandbox/default/root/var:/var