fix: readthedocs git fetch unshallow

[sbrunato]

Fixes issues when building readthedocs image: RTD performs a shallow git fetch with the last 50 commits, which prevented setuptools_scm to get eodag version and breaked its installation.
It is now configured to perform an unshallow git fetch

[github-actions]

Test Results

       4 files  ±0         4 suites  ±0   4m 28s ⏱️ -19s
   395 tests ±0     393 ✔️ ±0    2 💤 ±0  0 ❌ ±0 
1 580 runs  ±0  1 520 ✔️ ±0  60 💤 ±0  0 ❌ ±0 

Results for commit b443be5. ± Comparison against base commit e40b40d.

[github-actions]

Code Coverage (Ubuntu)

File	Coverage
All files	83%	✅

Minimum allowed coverage is 70%

Generated by 🐒 cobertura-action against b443be5

[github-actions]

Code Coverage (Windows)

File	Coverage
All files	77%	✅

Minimum allowed coverage is 70%

Generated by 🐒 cobertura-action against b443be5