git graph: don't show detached commits (#33645)

Current git graph is not usable for mirrors of repos having a lot of
PRs, as can be seen at
https://demo.gitea.com/ericLemanissier/conan-center-index/graph

![image](https://github.com/user-attachments/assets/ace40dd2-3eea-4d69-8e19-10fb7224e326)


Manually running `git log --graph --date-order --all` on such a repo
indeed shows:
```
*   commit c4a34bd39d7977c8630177c5f88507000ea3e943
|\  Merge: a4bbd3ad6b 35a102c77c
| | Author: toge <[email protected]>
| | Date:   Wed Feb 19 08:36:41 2025 +0000
| |
| |     Merge 35a102c77cbc38d84baca0ca63466fb410336ea8 into a4bbd3ad6bb5a0f8e5117a897d8c55941f533d98
| |
| * commit 35a102c77cbc38d84baca0ca63466fb410336ea8
| | Author: toge <[email protected]>
| | Date:   Wed Feb 19 17:36:35 2025 +0900
| |
| |     update 4.4.2
| |
| | * commit 5d610f4fd3c0428731e402a2f618fad9ce055875
| |/| Merge: a4bbd3ad6b fe916fb70a
|/| | Author: Antony Peacock <[email protected]>
| | | Date:   Wed Feb 19 08:31:30 2025 +0000
| | |
| | |     Merge fe916fb70a8bf49503cce70a5c7124bcc4314ddc into a4bbd3ad6bb5a0f8e5117a897d8c55941f533d98
| | |
| | * commit fe916fb70a8bf49503cce70a5c7124bcc4314ddc
| | | Author: Antony Peacock <[email protected]>
| | | Date:   Wed Feb 19 08:31:18 2025 +0000
| | |
| | |     Remove parquet cmakelist patch
| | |
| | | * commit 9f6d2759d650ec3c86d01bb940e829e7e14220c2
| |_|/| Merge: a4bbd3ad6b f0963429b0
|/| | | Author: Thomas Sedlmair <[email protected]>
| | | | Date:   Wed Feb 19 08:03:08 2025 +0100
| | | |
| | | |     Merge f0963429b0952499da0da7e559f8d53387097307 into a4bbd3ad6bb5a0f8e5117a897d8c55941f533d98
| | | |
| | | * commit f0963429b0952499da0da7e559f8d53387097307
| |_|/  Author: Thomas Sedlmair <[email protected]>
|/| |   Date:   Wed Feb 19 08:01:43 2025 +0100
| | |
| | |       added cwt-cucumber 2.5
| | |
```

On the other hand, running `git log --graph --date-order --branches
--tags` returns the expected:
```
* commit a4bbd3ad6bb5a0f8e5117a897d8c55941f533d98 (HEAD -> master)
| Author: Dan <[email protected]>
| Date:   Fri Feb 14 18:46:11 2025 +0200
|
|     grpc: add version 1.69.0 (#26446)
|
|     * grpc: add version 1.69.0
|
|     * add cmake tool requires
|
|     ---------
|
|     Co-authored-by: Luis Caro Campos <[email protected]>
|
* commit a7868807cb2e21206ebf95278cb588f29a3e2205
| Author: Guillaume Egles <[email protected]>
| Date:   Thu Feb 13 05:44:35 2025 -0800
|
|     openssl: add versions `3.0.16`, `3.1.8`, `3.2.4`, `3.3.3`, `3.4.1`, stop publishing revisions for version `3.0.15` (#26578)
|
* commit 86057d3e63ac71e2fe48c07bb301f2d54187044d
| Author: Luis Caro Campos <[email protected]>
| Date:   Thu Feb 13 13:34:41 2025 +0000
|
|     android-ndk: dont set LD and AS variables (#26581)
|
|     * android-ndk: dont set LD and AS variables
|
|     * android-ndk: refactor test package
|
* commit 123e382fafd2f5e811e10faac02efc275c45ec2a
| Author: Nikita <[email protected]>
| Date:   Thu Feb 13 12:29:39 2025 +0300
|
|     libffi: fix conditionals when building on Windows (#26500)
|
|     * fix: add missing or `clang`
|
|     * fix: libffi - always require as tool `automake`
```

Author: ericLemanissier

services/repository/gitgraph/graph.go

@@ -29,7 +29,7 @@ func GetCommitGraph(r *git.Repository, page, maxAllowedColors int, hidePRRefs bo
 	}
 
 	if len(branches) == 0 {
-		graphCmd.AddArguments("--all")
+		graphCmd.AddArguments("--tags", "--branches")
 	}
 
 	graphCmd.AddArguments("-C", "-M", "--date=iso-strict").