Fix building in detached state (issue #8) - #9

this derivation will be built:
  /nix/store/6qrgskrml98h7prnrgy7283p3s2q95jm-reuse-lint.drv
these 13 paths will be fetched (1.83 MiB download, 19.75 MiB unpacked):
  /nix/store/irwqwpb23r6hy1jwyzf2hr80im289wfm-file-5.45
  /nix/store/glyj7sfdha5c50x67xinxzlarzlr0yd9-python3.13-attrs-25.3.0
  /nix/store/10pqpbvvk22c7jsl5h91dy8nsdd7sphz-python3.13-binaryornot-0.4.4
  /nix/store/3363lyr5v1phs032hizv6hn7bvjrz20s-python3.13-boolean-py-5.0
  /nix/store/abvbd0fx8milk5li8n9hddhha44x3as9-python3.13-chardet-5.2.0
  /nix/store/9125mj218kpx6yavnxfy02lkg2dznddc-python3.13-charset-normalizer-3.4.3
  /nix/store/xjv3d4mkc9djknbqls7zk9r2y4s2kfyw-python3.13-jinja2-3.1.6
  /nix/store/lj1cnlay2dqv00m4ms0kafncaxm0jp4g-python3.13-license-expression-30.4.4
  /nix/store/k25afd3qplafhpnnyz0y60zchd4wpi79-python3.13-markupsafe-3.0.3
  /nix/store/3qqrzrvxaycw7vn2q4qjm8jz852k3rcd-python3.13-python-debian-1.0.1
  /nix/store/x44g6jg0jqfjw6m9sz3gnzs5myf1n0qm-python3.13-python-magic-0.4.27
  /nix/store/dqi8qs9w55wvmvmh2b3gw0w168bq37rr-python3.13-reuse-6.2.0
  /nix/store/6rdmcxwznj35bhk466grs98v6n5dbzzn-python3.13-tomlkit-0.13.3
reuse-lint> Running phase: unpackPhase
reuse-lint> unpacking source archive /nix/store/fg0kfjrp9b0yi4z98j267dchph7637dw-source
reuse-lint> source root is source
reuse-lint> Running phase: patchPhase
reuse-lint> Running phase: updateAutotoolsGnuConfigScriptsPhase
reuse-lint> Running phase: configurePhase
reuse-lint> no configure script, doing nothing
reuse-lint> Running phase: checkPhase
reuse-lint> # SUMMARY
reuse-lint> 
reuse-lint> * Bad licenses: 0
reuse-lint> * Deprecated licenses: 0
reuse-lint> * Licenses without file extension: 0
reuse-lint> * Missing licenses: 0
reuse-lint> * Unused licenses: 0
reuse-lint> * Used licenses: CC0-1.0, MIT
reuse-lint> * Read errors: 0
reuse-lint> * Invalid SPDX License Expressions: 0
reuse-lint> * Files with copyright information: 11 / 11
reuse-lint> * Files with license information: 11 / 11
reuse-lint> 
reuse-lint> Congratulations! Your project is compliant with version 3.3 of the REUSE Specification :-)
reuse-lint> Running phase: installPhase
reuse-lint> Running phase: fixupPhase
reuse-lint> shrinking RPATHs of ELF executables and libraries in /nix/store/cvwc14hf9mv45agj95v5avizywpp7a2g-reuse-lint
reuse-lint> checking for references to /build/ in /nix/store/cvwc14hf9mv45agj95v5avizywpp7a2g-reuse-lint...
reuse-lint> patching script interpreter paths in /nix/store/cvwc14hf9mv45agj95v5avizywpp7a2g-reuse-lint