Make go version check reliable by using double brackets (#10125)

For more complex integer operations in most modern shells you should
use double parens (shell uses let builtin) or double brackets (shell
uses test builtin) to ensure proper variable expansion and expression
execution (we explicitly use bash today in the build scripts).

In this case the lack of determinism and potential errors comes from
expansion of variables w/o a declared type (`declare -i number` or
`typeset -in`) or implicit type via e.g. `let foo=${bar}+0`. So if
we did not get a valid number from any of the regexp capture groups
(in my case I had go 1.18 installed so no patch version) then the
variable expansion can result in strings getting compared to numbers.
With the single brackets the go check does not work in this scenario
and we see this output from `make build`:
$ make build
Thu Apr 21 11:42:02 EDT 2022: Building source tree
./tools/shell_functions.inc: line 29: [: -lt: unary operator expected
./tools/shell_functions.inc: line 30: [: -gt: unary operator expected
./tools/shell_functions.inc: line 31: [: -lt: unary operator expected
./tools/shell_functions.inc: line 32: [: -gt: unary operator expected
./tools/shell_functions.inc: line 33: [: -lt: unary operator expected

The build will still complete but we do not enforce the go version as
intended. With this change we do (for example, in my case):
$ make build
Thu Apr 21 14:18:40 EDT 2022: Building source tree
ERROR: Go version reported: go version go1.18 darwin/arm64. Version 1.18.1+ required. See https://vitess.io/contributing/build-from-source for install instructions.
make: *** [build] Error 1

Signed-off-by: Matt Lord <mattalord@gmail.com>

tools/shell_functions.inc

@@ -26,11 +26,11 @@ function goversion_min() {
   wantmajor=${BASH_REMATCH[1]}
   wantminor=${BASH_REMATCH[2]}
   wantpatch=${BASH_REMATCH[3]}
-  [ "$gotmajor" -lt "$wantmajor" ] && return 1
-  [ "$gotmajor" -gt "$wantmajor" ] && return 0
-  [ "$gotminor" -lt "$wantminor" ] && return 1
-  [ "$gotminor" -gt "$wantminor" ] && return 0
-  [ "$gotpatch" -lt "$wantpatch" ] && return 1
+  [[ $gotmajor -lt $wantmajor ]] && return 1
+  [[ $gotmajor -gt $wantmajor ]] && return 0
+  [[ $gotminor -lt $wantminor ]] && return 1
+  [[ $gotminor -gt $wantminor ]] && return 0
+  [[ $gotpatch -lt $wantpatch ]] && return 1
   return 0
 }