Drop minimum required Git version to v2.24.0 again

In order to be able to make use of the reference-transaction hook in
Gitaly, the minimum required Git version was bumped to v2.28.0. But due
to a bug in the hook's implementation in git-core it cannot yet be used
reliably, and thus the new requirement doesn't make a lot of sense yet.
So let's remove the requirement and instead make v2.28.0 the recommended
version.

Note that previous requirements were inconsistent. Some parts noted that
Git v2.24.0 is required starting with GitLab 13.1, while other parts
said Git v2.25.0 is required. To avoid a retroactive bump, this commit
adjusts documentation to v2.24.0.

doc/install/installation.md

@@ -134,7 +134,7 @@ Make sure you have the right version of Git installed:
 # Install Git
 sudo apt-get install -y git-core
 
-# Make sure Git is version 2.28.0 or higher
+# Make sure Git is version 2.24.0 or higher (recommended version is 2.28.0)
 git --version
 ```
 

doc/install/requirements.md

@@ -56,7 +56,8 @@ The minimum required Go version is 1.13.
 
 From GitLab 13.1:
 
-- Git 2.28.x and later [is required](https://gitlab.com/gitlab-org/gitaly/-/issues/2959).
+- Git 2.24.x and later is required.
+- Git 2.28.x and later [is recommended](https://gitlab.com/gitlab-org/gitaly/-/issues/2959).
 
 ### Node.js versions
 

doc/update/README.md

@@ -224,8 +224,8 @@ possible.
 
 ### 13.3.0
 
-In 13.3.0, you must upgrade to at least Git v2.28. Previously, the minimum
-required version was Git v2.24.
+The recommended Git version is Git v2.28. The minimum required version of Git
+v2.24 remains the same.
 
 ### 13.2.0
 

doc/update/upgrading_from_source.md

@@ -124,7 +124,7 @@ rm go1.13.5.linux-amd64.tar.gz
 
 CAUTION: **Caution:**
 From GitLab 13.1, you must use at least Git v2.24 (previous minimum version was v2.22).
-From GitLab 13.3, you must use at least Git v2.28.
+Git v2.28 is recommended.
 
 To check you are running the minimum required Git version, see
 [Git versions](../install/requirements.md#git-versions).
@@ -132,7 +132,7 @@ To check you are running the minimum required Git version, see
 In Debian or Ubuntu:
 
 ```shell
-# Make sure Git is version 2.28.0 or higher
+# Make sure Git is version 2.24.0 or higher
 git --version
 
 # Remove packaged Git

lib/system_check/app/git_version_check.rb

@@ -7,7 +7,7 @@ module SystemCheck
       set_check_pass -> { "yes (#{self.current_version})" }
 
       def self.required_version
-        @required_version ||= Gitlab::VersionInfo.parse('2.28.0')
+        @required_version ||= Gitlab::VersionInfo.parse('2.24.0')
       end
 
       def self.current_version