[dockerfile] add fontconfig, to see if this is what causes errors on CI

E.g.:
https://gitlab.iscpif.fr/gargantext/haskell-gargantext/-/jobs/18643

paginating QuantumComputing corpus works (MapTerms):            Fontconfig error: Cannot load default config file: No such file: (null)
Fontconfig error: No writable cache directories
4 jobs for 483-dev-corenlp-in-nix-flake in 49 minutes and 33 seconds (queued for 1 second)
Status Job ID Name Coverage
  Cabal
passed #18648
cabal

00:22:59

 
  Stack
passed #18649
stack

00:02:17

 
  Bench
manual #18650
allowed to fail manual
bench
 
  Test
failed #18651
test

00:24:16

 
Name Stage Failure
failed
test Test
Test suite garg-test-hspec: FAIL
Test suite logged to:
/builds/gargantext/haskell-gargantext/dist-newstyle/build/x86_64-linux/ghc-9.6.6/gargantext-0.0.7.4.7/t/garg-test-hspec/opt/test/gargantext-0.0.7.4.7-garg-test-hspec.log
0 of 1 test suites (0 of 1 test cases) passed.
Error: [Cabal-7125]
Tests failed for test:garg-test-hspec from gargantext-0.0.7.4.7.

Cleaning up project directory and file based variables
ERROR: Job failed: exit code 1