Disable fast-fail to let CI actually run even though beta is broken

[TheBlueMatt]

CI is currently failing on rustc beta due to rust-lang/rust#86442 (comment)

[codecov]

Codecov Report

Merging #1021 (a7934d7) into main (f3b63e4) will not change coverage.
The diff coverage is n/a.

@@           Coverage Diff           @@
##             main    #1021   +/-   ##
=======================================
  Coverage   90.79%   90.79%           
=======================================
  Files          60       60           
  Lines       31434    31434           
=======================================
  Hits        28542    28542           
  Misses       2892     2892           

Impacted Files	Coverage Δ
lightning/src/ln/functional_tests.rs	97.30% <0.00%> (ø)

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