GitlabCI should fetch less from git

Here's example when fetch failed https://git.drupalcode.org/issue/drupal-3387400/-/jobs/88976

Cloud caching has downsides
- more data transfered from/to runner
- zipping cache before sending takes time and brings high load to caching server

Meantime I see #3386566: Add support for 'test only' changes to gitlab CI which also gonna diff changed files so this functionality can be extracted to before script for such jobs

Moreover the job should fail when it unable to find a lit of changed files

Added to IS about ${CI_COMMIT_BRANCH} which probably should not be used in scripts

it was added in #3386680-8: Run jobs on GitLab CI branch tests

Changed to fetch less to compare and fixed IS as TARGET_BRANCH=${CI_MERGE_REQUEST_TARGET_BRANCH_NAME}${CI_COMMIT_BRANCH} which works both for MRs and commits

The job fixes can't be moved to separate issue because it will fail

I did test it in https://git.drupalcode.org/issue/drupal-3252386/-/jobs/88908

Sorry the valid link is https://git.drupalcode.org/issue/drupal-3252386/-/jobs/88870

Job does not fail but doing nothing, it smells a new issue

it needs work for CI_MERGE_REQUEST_PROJECT_URL which is missing for commit/tag runs

Looks failure was random, on restart it passed

    Testing Drupal\Tests\Component\Utility\RandomTest
    ......E.....                                                      12 / 12
    (100%)
    
    Time: 00:00.032, Memory: 4.00 MB
    
    There was 1 error:
    
    1)
    Drupal\Tests\Component\Utility\RandomTest::testRandomMachineNamesUniqueness
    RuntimeException: Unable to generate a unique random machine name
    
    /builds/issue/drupal-3387400/core/lib/Drupal/Component/Utility/Random.php:169
    /builds/issue/drupal-3387400/core/tests/Drupal/Tests/Component/Utility/RandomTest.php:127
    /builds/issue/drupal-3387400/vendor/phpunit/phpunit/src/Framework/TestResult.php:728
    /builds/issue/drupal-3387400/vendor/phpunit/phpunit/src/Framework/TestSuite.php:684
    /builds/issue/drupal-3387400/vendor/phpunit/phpunit/src/TextUI/TestRunner.php:651
    /builds/issue/drupal-3387400/vendor/phpunit/phpunit/src/TextUI/Command.php:144
    /builds/issue/drupal-3387400/vendor/phpunit/phpunit/src/TextUI/Command.php:97
    
    ERRORS!
    Tests: 12, Assertions: 97, Errors: 1.
[31mFail      run-tests. Unknown              0 Unknown                            
[0m    FATAL Drupal\Tests\Component\Utility\RandomTest: test runner returned a
    non-zero error code (2).

+1 RTBC and using the variable in job, suggested the same to backport to D7 #3387052: [D7] GitLab CI integration for core

Some tests still running but what we fixing here is https://git.drupalcode.org/project/drupal/-/jobs/91306

$ export TARGET_BRANCH=${CI_MERGE_REQUEST_TARGET_BRANCH_NAME}${CI_COMMIT_BRANCH}
$ git fetch -vn --depth=$GIT_DEPTH "${CI_MERGE_REQUEST_PROJECT_URL:-origin}" "+refs/heads/$TARGET_BRANCH:refs/heads/$TARGET_BRANCH"
warning: redirecting to https://git.drupalcode.org/-/push_from_secondary/9/project/drupal.git/
POST git-upload-pack (334 bytes)
POST git-upload-pack (524 bytes)
From https://git.drupalcode.org/project/drupal
 * [new branch]        11.x       -> 11.x
$ export MODIFIED=`git diff --name-only refs/heads/$TARGET_BRANCH|while read r;do echo "$CI_PROJECT_DIR/$r";done|tr "\n" " "`
$ echo $MODIFIED | tr ' ' '\n' | yarn --cwd=./core run -s spellcheck:core --no-must-find-files --file-list stdin
1/1 /builds/project/drupal/.gitlab-ci.yml
 437.27ms
2/2 /builds/project/drupal/.gitlab-ci/pipeline.yml 88.84ms
CSpell: Files checked: 2, Issues found: 0 in 0 files