fix libgfortran version in auditor test

[t-bltg]

The official 1.7.3 version of julia for the x86_64-linux-gnu triplet ships with libgfortran.so.4:

julia> VERSION
v"1.7.3"
julia> using Libdl
julia> foreach(println, Libdl.dllist())
linux-vdso.so.1
/lib/x86_64-linux-gnu/libdl.so.2
/lib/x86_64-linux-gnu/libpthread.so.0
/lib/x86_64-linux-gnu/libc.so.6
[...]/bin/../lib/libjulia.so.1
/lib64/ld-linux-x86-64.so.2
[...]/bin/../lib/julia/libgcc_s.so.1
[...]/bin/../lib/julia/libopenlibm.so
[...]/bin/../lib/julia/libjulia-internal.so.1
[...]/bin/../lib/julia/libunwind.so.8
[...]/bin/../lib/julia/libLLVM-12jl.so
/lib/x86_64-linux-gnu/librt.so.1
[...]/bin/../lib/julia/libatomic.so.1
[...]/bin/../lib/julia/libstdc++.so.6
/lib/x86_64-linux-gnu/libm.so.6
[...]/bin/../lib/julia/libz.so.1
[...]/lib/julia/sys.so
[...]/bin/../lib/julia/libpcre2-8.so
[...]/bin/../lib/julia/libgmp.so
[...]/bin/../lib/julia/libmpfr.so
[...]/bin/../lib/julia/libopenblas64_.so
[...]/bin/../lib/julia/libgfortran.so.4  # <== here !
[...]/bin/../lib/julia/libquadmath.so.0
[...]/bin/../lib/julia/libblastrampoline.so
[...]/bin/../lib/julia/libcholmod.so
[...]/bin/../lib/julia/libamd.so.2
[...]/bin/../lib/julia/libcolamd.so.2
[...]/bin/../lib/julia/libsuitesparseconfig.so.5
[...]/bin/../lib/julia/libccolamd.so.2
[...]/bin/../lib/julia/libcamd.so.2
[...]/bin/../lib/julia/libnghttp2.so.14
[...]/bin/../lib/julia/libcurl.so
[...]/bin/../lib/julia/libssh2.so.1
[...]/bin/../lib/julia/libmbedtls.so.13
[...]/bin/../lib/julia/libmbedx509.so.1
[...]/bin/../lib/julia/libmbedcrypto.so.5

So this fails the test suite when using julia --project=. -e 'using Pkg; Pkg.test()' (of course version 1.7.3 is used here).

This PR allows either version 4 or 5 of libgfortran so that the testsuite passes locally.

Probably related to #686.

cc @giordano