fix checksum for GULP 6.1

[boegel]

(created using eb --new-pr)
fixes #15984

[jfgrimm]

Test report by @jfgrimm
FAILED
Build succeeded for 0 out of 1 (1 easyconfigs in total)
node109.pri.viking.alces.network - Linux CentOS Linux 7.9.2009, x86_64, Intel(R) Xeon(R) Gold 6138 CPU @ 2.00GHz (skylake_avx512), Python 3.6.8
See https://gist.github.com/b37c288898ce83446e4e3e587a9ac615 for a full test report.

[jfgrimm]

@boegel patch will need updating too

== FAILED: Installation ended unsuccessfully (build directory: /tmp/jfg508/GULP/6.1/foss-2021b): build failed (first 300 chars): Couldn't apply patch file 
/tmp/eb-wleqad0o/files_pr16423/g/GULP/GULP-6.1_fftw-blas-linking-gcc-11.patch. Process exited with code 1: patching file Src/mkgulp
Hunk #2 succeeded at 251 (offset 21 lines).
Hunk #3 FAILED at 238.
Hunk #4 FAILED at 247.
Hunk #5 succeeded at 371 (offset 8 lines).

[jfgrimm]

Test report by @jfgrimm
SUCCESS
Build succeeded for 1 out of 1 (1 easyconfigs in total)
node109.pri.viking.alces.network - Linux CentOS Linux 7.9.2009, x86_64, Intel(R) Xeon(R) Gold 6138 CPU @ 2.00GHz (skylake_avx512), Python 3.6.8
See https://gist.github.com/a37c818b1dde93d833676d8d2faf62ec for a full test report.

[jfgrimm]

LGTM

[jfgrimm]

Going in, thanks @boegel!