`nix build` failing - old `rustc`

[chrismazanec]

the project fails to build with nix build.

$ nix build
error: builder for '/nix/store/j732ph2z21q216z7dg9kbbh7kjkd1n4a-fm.drv' failed with exit code 101;
       last 18 log lines:
       > unpacking sources
       > unpacking source archive /nix/store/v08cm33c8dfq2ci29pjnqhdfhigib9yk-ag2hw2gcnvgnx2wm117sh0lvf1s41aag-source
       > source root is ag2hw2gcnvgnx2wm117sh0lvf1s41aag-source
       > Executing cargoSetupPostUnpackHook
       > Finished cargoSetupPostUnpackHook
       > patching sources
       > Executing cargoSetupPostPatchHook
       > Validating consistency between /build/ag2hw2gcnvgnx2wm117sh0lvf1s41aag-source/Cargo.lock and /build/cargo-vendor-dir/Cargo.lock
       > Finished cargoSetupPostPatchHook
       > updateAutotoolsGnuConfigScriptsPhase
       > configuring
       > building
       > Executing cargoBuildHook
       > ++ env CC_x86_64-unknown-linux-gnu=/nix/store/18bs92p6yf6w2wwxhbplgx02y6anq092-gcc-wrapper-12.3.0/bin/cc CXX_x86_64-unknown-linux-gnu=/nix/store/18bs92p6yf6w2wwxhbplgx02y6anq092-gcc-wrapper-12.3.0/bin/c++ CC_x86_64-unknown-linux-gnu=/nix/store/18bs92p6yf6w2wwxhbplgx02y6anq092-gcc-wrapper-12.3.0/bin/cc CXX_x86_64-unknown-linux-gnu=/nix/store/18bs92p6yf6w2wwxhbplgx02y6anq092-gcc-wrapper-12.3.0/bin/c++ cargo build -j 8 --target x86_64-unknown-linux-gnu --frozen --release
       > error: package `relm4-css v0.9.0` cannot be built because it requires rustc 1.75 or newer, while the currently active rustc version is 1.72.0
       > Either upgrade to rustc 1.75 or newer, or use
       > cargo update -p relm4-css@0.9.0 --precise ver
       > where `ver` is the latest version of `relm4-css` supporting rustc 1.72.0
       For full logs, run:
         nix log /nix/store/j732ph2z21q216z7dg9kbbh7kjkd1n4a-fm.drv
$