generate.sh should be robust to incorrect YAML files.

[Zimmi48]

Incorrect YAML files can lead to hard to decipher errors, or even completely strange behavior.
For instance, a meta.yml which contained the following incorrect part:

dependencies:
- opam:
    name: coq-coqeal
    version: '{>= "1.0.3"}'
    name: coq-mathcomp-real-closed
    version: '{>= "1.0.4"}'
    name"coq-mathcomp-bigenough '{>= "1.0.0"}'

(https://github.com/math-comp/apery/blob/57704e1e97be40be9ffc3ae77b2a894200804f87/meta.yml#L58-L64)

led, when running generate.sh (with the mustache-go implementation) to:

mkdir: création du répertoire '.circleci'
Generating .circleci/config.yml...
mkdir: création du répertoire '.github'
mkdir: création du répertoire '.github/workflows'
Generating .github/workflows/coq-action.yml...
Generating Error: yaml: line 64: could not find expected ':'.opam...
Generating default.nix...
Generating Error: yaml: line 64: could not find expected ':'.opam...
Generating index.md...
Generating README.md...
Generating .travis.yml...

and to the creation of 4 files (default.nix, index.md, README.md and... Error: yaml: line 64: could not find expected ':'.opam") which all contained:

Error: yaml: line 64: could not find expected ':'