Update nounwind-macros to v0.1.7

Changed

• Updated nounwind-macros to syn v3.0 (vtyrwsts)
• Increased nounwind-macros MSRV to v1.71 to match syn (vtyrwsts)

Fixed

• In examples and tests, avoid using format! with local variable references. (nllntsny)
  • Fixes examples and tests failing to compile on the MSRV of 1.56.
  • This issue cannot affect any of our dependencies.
• ci: Ensure we test the nounwind MSRV of 1.56 (1.56).
  • Before this, we were only testing the newer unwind-macro MSRV of 1.61.
  • Thankfully, the already published code for v0.1.6 works just fine on 1.56,
    the only compilation issue was with an example.
• ci: Fix newer syn dependencies breaking the build on Rust 1.56 (zrnmspqo)

This is the first release of nounwind-macros since v0.1.1.