build: Run staticcheck with "go run"

Running the tool this way ensures that we'll always run the version
selected by our go.mod file, rather than whatever happened to be available
in $GOPATH/bin on the system where we're running this.

This change caused some contexts to now be using a newer version of
staticcheck with additional checks, and so this commit also includes some
changes to quiet the new warnings without any change in overall behavior.

internal/lang/funcs/cidr_test.go

@@ -246,7 +246,7 @@ func TestCidrSubnet(t *testing.T) {
 		},
 		{ // fractions are Not Ok
 			cty.StringVal("10.256.0.0/8"),
-			cty.NumberFloatVal(2 / 3),
+			cty.NumberFloatVal(2.0 / 3.0),
 			cty.NumberFloatVal(.75),
 			cty.UnknownVal(cty.String),
 			true,

internal/plugin/discovery/find.go

@@ -154,9 +154,7 @@ func ResolvePluginPaths(paths []string) PluginMetaSet {
 
 		// Trim the .exe suffix used on Windows before we start wrangling
 		// the remainder of the path.
-		if strings.HasSuffix(baseName, ".exe") {
-			baseName = baseName[:len(baseName)-4]
-		}
+		baseName = strings.TrimSuffix(baseName, ".exe")
 
 		parts := strings.SplitN(baseName, "_v", 2)
 		name := parts[0]

scripts/staticcheck.sh

@@ -13,4 +13,4 @@ packages=$(go list ./... | egrep -v ${skip})
 # We are skipping style-related checks, since terraform intentionally breaks
 # some of these. The goal here is to find issues that reduce code clarity, or
 # may result in bugs.
-staticcheck -checks 'all,-ST*' ${packages}
+go run honnef.co/go/tools/cmd/staticcheck -checks 'all,-ST*' ${packages}