docker/fedora: run git gc after cloning the subprojects

Most of the subprojects specify depth=1 in the wrap file,
so this doesn't have a big effect atm.

Part-of: <!375>
41 jobs for master in 20 minutes and 32 seconds (queued for 13 seconds)
Status Job ID Name Coverage
  Build Docker
passed alpine amd64 manifest builder docker #6920286

00:00:15

passed android docker #6920285

00:00:16

passed cerbero fedora amd64 docker #6920284

00:00:16

passed fedora amd64 docker #6920283

00:20:20

passed gst-indent amd64 docker #6920287

00:00:21

passed test manifest amd64 docker #6920288

00:00:12

 
  Preparation
passed gst indent #6920290

00:00:08

manual manifest #6920289
manual
passed test manifest #6920291

00:00:11

 
  Build
created build cerbero cross-android universal #6920300
gstreamer
created build cerbero cross-ios universal #6920304
gst-ios-14.3
created build cerbero cross win32 #6920301
gstreamer
created build cerbero cross win64 #6920302
gstreamer
created build cerbero fedora x86_64 #6920299
gstreamer
created build cerbero macos x86_64 #6920303
gst-macos-11.1
created build cerbero msvc x86_64 #6920307
docker windows gstreamer-windows 1809
created build clang fedora x86_64 #6920295
created build gst-omx tizonia fedora x86_64 #6920306
created build gst-omx zynq fedora x86_64 #6920305
created build msys2 #6920298
docker windows 1809 allowed to fail manual
created build nodebug fedora x86_64 #6920292
created build static fedora x86_64 #6920293
created build static nodebug fedora x86_64 #6920294
created build vs2017 amd64 #6920296
docker windows 1809
created build vs2017 x86 #6920297
docker windows 1809
 
  Test
created check fedora #6920308
gstreamer
created integration testsuites fedora 1/4 #6920309
gstreamer
created integration testsuites fedora 2/4 #6920310
gstreamer
created integration testsuites fedora 3/4 #6920311
gstreamer
created integration testsuites fedora 4/4 #6920312
gstreamer
created valgrind bad #6920317
gstreamer
created valgrind base #6920314
gstreamer
created valgrind core #6920313
gstreamer
created valgrind ges #6920318
gstreamer
created valgrind good #6920315
gstreamer
created valgrind ugly #6920316
gstreamer
 
  Integrate
created cross-android universal examples #6920321
created cross-ios universal examples #6920323
gst-ios-14.3
created documentation #6920322
created gstreamer-full #6920319
created gstreamer-full-minimal #6920320