tarball: include .cargo/config.toml again

The problem worked around by commit e4674cd7b5 (.cargo/config.toml:
exclude from tarball, 2025-01-12) is as follows:
our OBS packages are built by doing something like

	tar xf $tarball && tar xf $vendor_tarball

except that the tool apparently break when a file is present in
both tarballs.

Our workaround is to not include .cargo/config.toml in the tarball.

The workaround seems too broad. It need not affect all tarballs
but only the ones used by OBS. We want to add xtask aliases to
.cargo/config.toml. They will be used by CMake targets (sphinx-doc),
so they should be available to tarball consumers.

Restrict the scope of the workaround: add back .cargo/config.toml
to the export, and allow opting in to this behavioer by passing a
negative pathspec

	build_tools/make_tarball.sh :/!.cargo/config.toml

.gitattributes

@@ -18,9 +18,6 @@
 /.github/* export-ignore
 /.builds export-ignore
 /.builds/* export-ignore
-# to make cargo vendor work correctly
-/.cargo/ export-ignore
-/.cargo/config.toml export-ignore
 
 # for linguist, which drives GitHub's language statistics
 alpine.js linguist-vendored

build_tools/make_tarball.sh

@@ -3,6 +3,10 @@
 # Script to generate a tarball
 # Outputs to $FISH_ARTEFACT_PATH or ~/fish_built by default
 
+# Example usage:
+#
+#   build_tools/make_tarball.sh :/!.cargo/config.toml
+
 # Exit on error
 set -e
 
@@ -14,7 +18,7 @@ path=${FISH_ARTEFACT_PATH:-~/fish_built}/$prefix.tar.xz
 
 git archive \
     --prefix="$prefix/" \
-    HEAD |
+    HEAD "$@" |
     xz >"$path"
 
 # Output what we did, and the sha256 hash

build_tools/make_vendor_tarball.sh

@@ -42,8 +42,14 @@ rm -f "$path" "$path".xz
 PREFIX_TMPDIR=$(mktemp -d)
 cd "$PREFIX_TMPDIR"
 
+# Add .cargo/config.toml. This means that the caller may need to remove that file from the tarball.
+# See e4674cd7b5f (.cargo/config.toml: exclude from tarball, 2025-01-12)
+
 mkdir .cargo
-cargo vendor --manifest-path "$wd/Cargo.toml" >> .cargo/config.toml
+{
+    cat "$wd"/.cargo/config.toml
+    cargo vendor --manifest-path "$wd/Cargo.toml"
+} > .cargo/config.toml
 
 tar cfvJ "$path".xz vendor .cargo