build: fix missing '!' in shebang of generated oss-fuzz scripts (#34044)

\`oss-fuzz.sh\` line 38 writes \`#/bin/sh\` instead of \`#!/bin/sh\` as
the shebang of generated fuzz test runner scripts.

\`\`\`diff
-#/bin/sh
+#!/bin/sh
\`\`\`

Without the \`!\`, the kernel does not recognize the interpreter
directive.

Co-authored-by: Claude Opus 4.6 <noreply@anthropic.com>

oss-fuzz.sh

@@ -35,7 +35,7 @@ function coverbuild {
   sed -i -e 's/TestFuzzCorpus/Test'$function'Corpus/' ./"${function,,}"_test.go
 
 cat << DOG > $OUT/$fuzzer
-#/bin/sh
+#!/bin/sh
 
   cd $OUT/$path
   go test -run Test${function}Corpus -v $tags -coverprofile \$1 -coverpkg $coverpkg