chore: update Go to v1.27 (#39068)

Only made some necessary changes:

1. remove `GOEXPERIMENT`, only use jsonv2
1. `make fmt`
* `SigningKey` and `Signature` were affected due to some bugs in the
toolchain, so rewrote them
1. remove or fix fragile magic numbers and strings
    * the outputs of image/gzip/zlib packages are different
1. update "nolint" comments for the changed lint behaviors
1. add `tls.MLKEM1024`

.github/workflows/pull-db-tests.yml

@@ -96,7 +96,6 @@ jobs:
       - run: make backend
         env:
           TAGS: bindata gogit
-          GOEXPERIMENT:
       - run: GITEA_TEST_DATABASE=sqlite make test-migration
         env:
           TAGS: bindata gogit
@@ -107,7 +106,6 @@ jobs:
           # sqlite driver can contain large amount of Golang code, so don't use race detector for it, otherwise, extremely slow
           GOTEST_FLAGS: -timeout=40m
           TAGS: bindata gogit
-          GOEXPERIMENT:
 
   test-unit:
     if: needs.files-changed.outputs.backend == 'true'
@@ -170,7 +168,6 @@ jobs:
         env:
           GOTEST_FLAGS: -race -timeout=20m
           TAGS: bindata gogit
-          GOEXPERIMENT:
           GITHUB_READ_TOKEN: ${{ secrets.GITHUB_READ_TOKEN }}
           GITEA_TEST_CI_SKIP_EXTERNAL: true
       - run: make test-check