some test failed on v1.7.7 tags & go1.17

[WangLeonard]

git checkout v1.7.7
go test ./...

Description

## Expectations

all passed

## Actual result

```bash
=== RUN   TestContextRenderFile
    context_test.go:1008: 
        	Error Trace:	context_test.go:1008
        	Error:      	Not equal: 
        	            	expected: "text/plain; charset=utf-8"
        	            	actual  : "text/x-go; charset=utf-8"
        	            	
        	            	Diff:
        	            	--- Expected
        	            	+++ Actual
        	            	@@ -1 +1 @@
        	            	-text/plain; charset=utf-8
        	            	+text/x-go; charset=utf-8
        	Test:       	TestContextRenderFile
--- FAIL: TestContextRenderFile (0.00s)


Expected :text/plain; charset=utf-8
Actual   :text/x-go; charset=utf-8

=== RUN   TestContextRenderFileFromFS
    context_test.go:1020: 
        	Error Trace:	context_test.go:1020
        	Error:      	Not equal: 
        	            	expected: "text/plain; charset=utf-8"
        	            	actual  : "text/x-go; charset=utf-8"
        	            	
        	            	Diff:
        	            	--- Expected
        	            	+++ Actual
        	            	@@ -1 +1 @@
        	            	-text/plain; charset=utf-8
        	            	+text/x-go; charset=utf-8
        	Test:       	TestContextRenderFileFromFS
--- FAIL: TestContextRenderFileFromFS (0.00s)


Expected :text/plain; charset=utf-8
Actual   :text/x-go; charset=utf-8

Environment

• go version: go version go1.17.3 linux/amd64
• gin version (or commit ref): v1.7.7
• operating system:

maybe missed 77649bc on v1.7.7

[Bisstocuz]

@thinkerou

[thinkerou]

1. chore(docs): Bump to v1.7.7 #2952 test ok
2. on my mac, run make test ok
3. on my mac, run go test ./... ok

➜  gin-1.7.7 go test ./...
ok  	github.com/gin-gonic/gin	1.102s
ok  	github.com/gin-gonic/gin/binding	0.441s
?   	github.com/gin-gonic/gin/ginS	[no test files]
ok  	github.com/gin-gonic/gin/internal/bytesconv	0.437s
?   	github.com/gin-gonic/gin/internal/json	[no test files]
ok  	github.com/gin-gonic/gin/render	0.845s

[WangLeonard]

@thinkerou Hi, This test case can indeed be passed on the mac.
I reproduced it on linux.
And $GOROOT/src/mime/type.go TypeByExtension will be different return value on linux and mac
mac

linux

I'm not sure about the further reason for this. My environment problem or go problem or gin problem.

[shawndx]

Thought it's related to a go sdk change, https://go-review.googlesource.com/c/go/+/305230, which supports "Shared MIME-info Database on Unix systems" in go1.17